{
  "id": "breast-cancer",
  "title": "Breast cancer",
  "lang": "en",
  "source_lang": "en",
  "summary": "Breast cancer is a malignant growth of breast cells, the most common cancer in women worldwide, with major variation in subtype, treatment and outcome.",
  "category": "health",
  "subcategory": "diseases",
  "type": "concept",
  "aliases": [
    "breast carcinoma",
    "mammary carcinoma",
    "breast neoplasm"
  ],
  "generated_at": "2026-10-15",
  "model": "pro/claude-haiku-5-5",
  "url": "https://aiwiki.page/en/breast-cancer/",
  "translations": {
    "zh-Hans": {
      "url": "https://aiwiki.page/zh/breast-cancer/",
      "json": "https://aiwiki.page/zh/breast-cancer.json"
    }
  },
  "sections": [
    {
      "heading": "",
      "text": "Breast cancer is a malignant tumour that arises from the epithelial cells of the breast, most often in the ducts or lobules that carry and produce milk. It is the most frequently diagnosed cancer among women worldwide. According to the World Health Organization, breast cancer caused an estimated 694 000 deaths globally in 2024. The disease is not a single entity. It spans non-invasive lesions, several histological types and multiple molecular subtypes, and each of these has different biology, prognosis and therapeutic options. Understanding it therefore requires links to cancer, cell, mutation and gene-expression.\n\nThe entry explains how breast cancer is defined and counted, why it develops and how it is classified, and how it is detected, staged and treated. Epidemiological material covers global incidence, mortality, risk factors and hereditary predisposition, including genetics. The clinical sections cover biopsy, pathology, surgery, radiation-therapy, hormone-based drugs, antibody-based therapies, chemotherapy and cancer-immunotherapy. The later sections address metastatic disease, survivorship, health policy and equity, and unresolved questions in screening and treatment de-escalation."
    },
    {
      "heading": "Definition, anatomy and terminology",
      "text": "The breast is composed of three main tissue components. Lobules are clusters of glandular acini that produce milk, ducts carry that milk to the nipple, and stroma, the fibrous, fatty and vascular connective tissue, surrounds and supports both. Most breast cancers arise from the epithelial lining of the lobules or ducts, so the site of origin largely determines the tumour's name and behaviour. Ductal carcinomas develop in the ducts and lobular carcinomas in the lobules, and the two differ in growth pattern, imaging appearance and patterns of spread.\n\nBreast cancer is a malignant proliferation of breast epithelial cells that has acquired the capacity to invade surrounding tissue. The defining features are uncontrolled cell growth, loss of normal tissue architecture and, in invasive forms, passage through the basement membrane into the stroma. This separates it from benign breast conditions such as fibroadenomas, cysts and simple hyperplasia, which proliferate without invading. It is also separate from non-epithelial tumours of the breast, such as sarcomas and lymphomas, which arise from connective or haematopoietic tissue and are managed under different principles.\n\nMale breast cancer is uncommon, accounting for roughly 1% of all breast cancers. Because male breast tissue is small and undeveloped, the disease has a different risk profile in part: it is more closely associated with inherited mutations (notably in BRCA2), with conditions that alter sex hormone balance such as Klinefelter syndrome, and with older age at diagnosis. Its research base is also much thinner. Most large randomised trials enrolled women, so many treatment decisions for men rest on evidence extrapolated from the female disease rather than on data gathered in men.\n\nSeveral terms are used with fixed meanings throughout this entry. \"In situ\" describes neoplastic epithelial cells confined within the duct or lobule, without having breached the basement membrane; ductal carcinoma in situ and lobular carcinoma in situ are the principal examples. \"Invasive\" (or infiltrating) describes tumour cells that have crossed the basement membrane and infiltrate the stroma, and invasive carcinoma of no special type is the most common form. \"Metastatic\" describes disease that has spread to distant organs or tissues, which corresponds to stage IV in the TNM system. Involvement of regional lymph nodes, such as the axillary, internal mammary or supraclavicular nodes, is classified as regional spread rather than distant metastasis. \"Recurrence\" refers to the return of disease after a period of remission, and is further specified as local, regional or distant.\n\nAssignment of these categories depends on examination of tissue by a pathologist using a biopsy or surgical specimen, which is why the terms are defined by histological and anatomical criteria rather than by clinical impression. Throughout the entry, \"carcinoma\" denotes an epithelial malignancy and \"sarcoma\" a mesenchymal one, and \"lesion\" is used for non-invasive or pre-invasive abnormalities, while \"tumour\" refers to an invasive or established neoplasm."
    },
    {
      "heading": "Global burden and epidemiology",
      "text": "Estimates for 2022 place the worldwide total at about 2.3 million new cases and roughly 666,000 deaths. In 2022, approximately 2.30 million new breast cancer cases and 666,103 deaths were reported globally. These figures come from the GLOBOCAN database, which is managed by the International Agency for Research on Cancer (IARC). Among women, the disease is the most frequently diagnosed cancer: breast cancer constitutes 23.8% (2,296,840/9,664,889) of new cases and 15.4% (666,103/4,313,548) of deaths. Across both sexes, the picture is different. Female breast cancer ranks second leading cause of global cancer incidence in 2022, with an estimated 2.3 million new cases, comprising 11.6% of all cancer cases, and it is the fourth leading cause of cancer mortality worldwide. The gap between these two ranks reflects a relatively high rate of diagnosis combined with a comparatively lower rate of death.\n\nThe burden is unevenly distributed. In absolute terms, Asia carries the largest load, with 985,817 cases, followed by Europe (557,532) and Northern America (306,307). Relative to population, however, incidence is highest in wealthier regions. The global age-standardized incidence rate of breast cancer in females is estimated at 48 per 100,000, ranging from below 30 per 100,000 in sub-Saharan Africa to over 70 per 100,000 in Western Europe and North America. Mortality tells a different story. The mortality-to-incidence ratio (MIR), calculated as deaths divided by new cases, serves as a rough proxy for survival disparities, and Africa recorded the highest mortality-to-incidence ratio (MIR) of 0.510, highlighting challenges in early detection and treatment. Low-HDI countries show an even higher ratio, highest in low HDI countries (0.533), reflecting survival disparities. For comparison, one analysis reports that the ratio remains alarmingly high at 0.55 in Central Africa, compared to just 0.16 in the United States. Although the relative incidence is highest in more developed regions, the larger populations in less developed regions result in over half of all breast cancer cases being diagnosed in low- and middle-income countries.\n\nProjections point to a substantial increase. If current patterns persist, one GLOBOCAN-based analysis estimates that breast cancer cases may rise to 3.55 million and deaths to 1.14 million by 2050. A separate IARC analysis published in 2025 gives a smaller relative rise: global breast cancer incidence is projected to rise by 38% and related deaths by 68% by 2050 if current rates continue. The two sets of figures differ in their baselines and methods, so the absolute numbers should be read with that in mind. Several factors drive the rising counts. Demographic change is the largest: a Global Burden of Disease analysis found that decomposition analysis highlighted demographic factors as the main drivers of increased disease burden over the past three decades. Ageing matters because incidence rates rise with age, and the largest projected increases in cases are in low-HDI countries, where an estimated increase of 327.28% is anticipated. Changing risk-factor prevalence adds to this, including delayed childbearing, lower fertility rates, shorter breastfeeding durations, obesity, and alcohol consumption.\n\nTrends over time show a divergence between incidence and mortality. Across 1990 to 2021, incidence and prevalence increased, while mortality and disability‐adjusted life years (DALYs) declined overall. The decline in deaths has been concentrated in wealthy countries. High-income countries have made significant progress in reducing age-standardized breast cancer mortality by 40% over the past 4 decades. Progress has been slower elsewhere: significant challenges remain in tackling the less favourable mortality rates in less developed countries. Projections for low- and middle-income countries suggest that age-standardized mortality could increase in 33 and 35 LMICs respectively by 2050, which would reverse the earlier trend in some settings.\n\nMen account for only a small fraction of cases. One clinical source notes that approximately, 0.5%-1% of BCs occur in men. Because of this small share, headline counts are typically reported as female breast cancer; in GLOBOCAN tables, the site is listed as \"Female breast\", so male cases are generally not separated out in the main totals. Sex-specific risk patterns also differ: in a GBD 2021 analysis, female DALY burden was predominantly driven by metabolic risks (e.g., high BMI), while male burden was overwhelmingly attributable to high alcohol consumption."
    },
    {
      "heading": "Risk factors and modifiable exposures",
      "text": "Non-modifiable factors\n\nSex is the strongest single determinant of breast cancer risk: the disease is overwhelmingly one of women, and incidence rises with age. Reproductive history is the best-studied group of non-modifiable factors. In the French E3N cohort of around 100,000 women, each additional year at menarche was associated with roughly a 3% lower risk, and a first full-term pregnancy after age 30 carried a risk ratio of about 1.6 before menopause and 1.35 after it. Nulliparity, late menopause and a late first birth have each been linked to higher risk in other cohort and case-control studies, while higher parity and breastfeeding are generally associated with lower risk. Parity has a dual pattern: a transient rise in risk around the time of childbirth, followed by longer-term protection that grows with the number of full-term pregnancies. Some of these associations may be confounded by the timing of menarche and menopause. Mendelian randomisation analyses have found only limited evidence for a causal protective effect of earlier first birth, so the causal interpretation remains debated. Family history is a further established risk factor, with its genetic basis covered in the hereditary section.\n\nHormonal exposures\n\nMenopausal hormone therapy is among the best-documented modifiable exposures. A Norwegian nationwide cohort of about 1.3 million women aged 45 and over found that current use of oral oestradiol combined with a progestin carried a hazard ratio of 2.42, and that risk rose with duration of use, reaching about 3.5 after more than five years of oral oestradiol-norethisterone use. Risk was higher with oral than with transdermal preparations in several analyses, and vaginal oestradiol showed no association. In the same data, the excess risk was greater for luminal A tumours and for interval rather than screen-detected cancers. Risk appears to fall after cessation but has been observed to persist for up to about ten years. The Women's Health Initiative combined-therapy arm, which enrolled older women, reported a smaller hazard ratio of 1.28.\n\nOral contraceptives show a much smaller association. Current use is linked to a modest increase in breast cancer risk, but the absolute risk in young women with low baseline rates is small, and use is also associated with reduced risk of ovarian, endometrial and colorectal cancers. Among postmenopausal women, previous oral contraceptive use has not been associated with increased breast cancer risk. More broadly, the cumulative duration of endogenous oestrogen exposure, reflected in early menarche, late menopause, few pregnancies and possibly the number of menstrual cycles, is thought to contribute to risk.\n\nLifestyle factors\n\nAlcohol is a convincing cause of postmenopausal breast cancer according to the World Cancer Research Fund's review. A dose-response meta-analysis found about a 9% increase in risk per 10 grams of ethanol per day, and no threshold has been identified below which risk is absent. The association is stronger for oestrogen receptor-positive tumours.\n\nBody fatness acts in opposite directions before and after menopause. After menopause, greater body fatness throughout adulthood, weight gain in adult life and higher attained height are associated with increased risk, and the mechanism is thought to involve adipose tissue, which produces oestrogen from androgens through the aromatase enzyme and is therefore an important oestrogen source in postmenopausal women. Higher body weight in young adulthood, by contrast, appears protective against postmenopausal disease. Physical activity is associated with lower risk, with the strongest reductions seen for regular, moderate-to-vigorous activity, activity sustained over a lifetime and activity in the postmenopausal years. Dietary evidence is generally weaker than that for alcohol, body weight and activity. Limited evidence suggests a possible role for calcium and non-starchy vegetables, but no dietary pattern has been established as a strong determinant. Population attributable estimates for the United States suggest that physical inactivity and high alcohol intake each account for a small but measurable share of postmenopausal invasive cancers.\n\nCases without a specific risk factor\n\nMost breast cancers arise in women who have none of the strongly established risk factors beyond sex and age. Individually, most identified exposures carry relative risks well below those seen for high-penetrance mutations, so the known factors explain only part of the variation in incidence. This pattern suggests that many cases reflect the combined effect of numerous small influences, including cumulative hormonal exposure, lifestyle and inherited variants of small effect, together with random somatic mutations that accumulate with age. It also means that primary prevention based on modifiable exposures can reduce the population burden without eliminating cancers in women who have no identifiable risk."
    },
    {
      "heading": "Hereditary and genetic predisposition",
      "text": "Inherited susceptibility accounts for only a minority of breast cancers. Approximately 10% of breast cancer cases are hereditary, and germline pathogenic variants in BRCA1 account for nearly 35% of these. Within hereditary breast-ovarian cancer syndromes, the two major genes are BRCA1 and BRCA2, which encode DNA-repair proteins that work together in repairing DNA.\n\nBRCA1, BRCA2 and other high-penetrance genes\n\nCarriers of inherited BRCA variants face much higher risks than the general population. The estimated cumulative risks of breast cancer by age 70 years in two meta-analyses were 55% to 65% for carriers of BRCA1 pathogenic variants and 45% to 47% for carriers of BRCA2 pathogenic variants. Extending the horizon to age 80, BRCA1 carriers have the highest lifetime burden of any known breast cancer gene, with projections near seven in ten. Risks in men are far lower but still elevated: up to 1.2% of men with a BRCA1 mutation and between 1.8% and 7.1% with a BRCA2 mutation will develop breast cancer by age 70, while only about 0.1% of men in the general population do so.\n\nBRCA-associated cancers also recur more often in the opposite breast. In the 20 years after their first diagnosis, about 30%-40% of women with a BRCA1 mutation and about 25% of women with a BRCA2 mutation will develop cancer in the opposite breast. BRCA1-associated tumours also lean toward the triple-negative phenotype (see the molecular subtypes section).\n\nPALB2 is the best-studied of the other genes. Its classification varies between sources: the NCI summary lists it among high-penetrance genes, whereas other groups describe it as moderate-risk. Estimated lifetime risk is 33–58%, and the figure is higher in younger women and those with a family history of breast cancer. TP53 variants cause Li-Fraumeni syndrome, in which the encoded protein normally restrains cell growth when DNA is damaged. Other genes, including ATM, BRIP1, CHEK2, FANCD2 and RAD51C, are generally classed as moderate-penetrance. Multigene panel testing has shown that pathogenic variants in BARD1, PALB2, and RAD51D, in addition to BRCA1 and BRCA2, were each associated with more than a fivefold increase in breast cancer.\n\nFamily history and testing criteria\n\nFamily history is the main practical trigger for genetic evaluation. Protein-truncating mutations in ATM, BRIP1, BRCA2, PALB2, and CHEK2 have been observed to be nearly 10 times more likely in patients with strong breast cancer family histories than in unaffected controls. Individuals with relevant personal or family histories are usually referred for genetic counselling and gene panel testing according to national guidelines. Counselling before and after testing addresses what results mean for relatives, how cascade testing works, and which surveillance or surgical options are open.\n\nA negative result does not always settle the question. Testing negative for a mutation linked to breast cancer can be uninformative; a 2026 study found that women with an uninformative negative BRCA result had a 25% lifetime risk of developing breast cancer.\n\nImplications for prevention and treatment\n\nHereditary status changes preventive decisions. In early cohorts, bilateral total or subcutaneous mastectomy suggested a 90–95% relative risk reduction in BRCA1/2 carriers electing for preventive breast surgery. Timing matters: a 70-year-old unaffected BRCA1/2 or PALB2 carrier harbors less than a 30% residual breast cancer risk to the age of 80 and may wish to consider enhanced surveillance over surgical prophylaxis. Surveillance for high-risk women often combines methods; one prospective programme screened carriers annually with breast magnetic resonance imaging (MRI) in addition to mammography. Germline status also shapes surgical choices in patients already diagnosed: patients with breast cancer and moderate penetrance gene mutations (ATM, CHEK2, or PALB2) were more likely to undergo a total mastectomy and contralateral risk-reducing mastectomy than those without mutations. Germline status also informs systemic therapy choices, which are covered in the systemic therapy section.\n\nPolygenic risk scores and small-effect variants\n\nMany common variants each add only a small amount of risk. Multiple common breast cancer susceptibility variants discovered through genome-wide association studies confer small risk individually, but their combined effect, when summarized as a polygenic risk score (PRS), can be substantial. Such scores are built by combining many single-nucleotide polymorphisms, and in one estimate the lifetime risk of overall breast cancer in the top centile of the PRSs was 32.6%. Discrimination is nonetheless modest: in one development study, the best score reached an area under the receiver-operator curve of 0.630.\n\nResearch has examined how PRS might sit alongside family history and known pathogenic variants. A Finnish study that linked scores to outcomes in a national screening programme covered 117,252 women. A separate analysis reported that while <1% of unaffected women unselected for family history would be identified for high-risk screening programs because of a pathogenic variant (such as in BRCA1, BRCA2, or PALB2), a polygenic risk score (PRS) can be calculated in all. Whether PRS should guide clinical decisions remains under evaluation, and surveys suggest that limited knowledge of PRS and risk-stratified screening exists among general practitioners."
    },
    {
      "heading": "Carcinogenesis and tumour biology",
      "text": "From normal epithelium to invasive cancer\n\nBreast carcinogenesis is usually described as a multistep process. Pathologists trace a route that starts in ordinary ductal epithelium, passes through hyperplasia and atypical hyperplasia, and then reaches in situ carcinoma before invasion The multistep model of carcinogenesis in the breast suggests a transition from normal epithelium to invasive carcinoma via non-atypical and atypical hyperplasia and in situ carcinoma. Each stage is generally thought to carry a greater chance of malignancy than the one before it each of which has a greater probability of becoming malignant than the one that preceded it. Each transition depends on the accumulation of somatic mutations in DNA and on epigenetic changes that switch gene expression on or off without altering the sequence itself.\n\nSome of these changes can be measured along the sequence. In one study, fluorescence counts of chromosome 1 rose from about 1.1 signals per normal nucleus to about 1.6 in hyperplasia and about 1.95 in ductal carcinoma in situ (DCIS) The mean signal number for normal cells was 1.14, while that for hyperplasia was 1.56 and ADH was 1.5, while values for DCIS of 1.95 and invasive duct carcinoma of 1.79, were higher. Epigenetic silencing appears early as well. Methylation of tumour suppressor gene promoters was found in 16 of 17 patients with mixed benign and malignant lesions, Epigenetic alterations, in particular promoter hypermethylation, are proving to be consistent and early events in neoplastic progression.\n\nThe linear model is not universally accepted. Accumulating data are inconsistent with this theory, and a competing \"parallel disease\" model proposes that low-grade DCIS tends to progress to low-grade IBC, with high-grade lesions following a separate path. The natural history of DCIS illustrates the uncertainty. In untreated cases, 25–60% DCIS progress to invasive ductal carcinoma, and the challenge lies in distinguishing between non-progressive and progressive DCIS, often resulting in over- or under-treatment. Sequencing of synchronous DCIS and invasive tumours found high genomic concordance between synchronous DCIS and IBC (52 out of 92 mutations were present in both components). However, the remaining mutations (40 out of 92) were restricted to the invasive component. This pattern suggests that progression from DCIS to IBC could be driven by the selection of subclones with specific genetic aberrations.\n\nClonal evolution and intratumour heterogeneity\n\nTumours are not uniform masses of identical cells. The clonal evolution model holds that although most neoplasms arise from a single cell, cancer cells have varying degrees of genetic instability and acquire additional genetic aberrations during tumorigenesis and tumor evolution. The result is a population made of several subclones, each carrying private changes on top of the founding events. Sequencing studies distinguish mutations present in nearly all tumour cells from subclonal ones. Both clonal mutations (e.g. mutations in TP53 and PIK3CA), which occurred in all tumor cells, and subclonal mutations, which only occurred in a subset of tumor cells, were observed. The number of subclonal mutations was much greater than the number of clonal mutations.\n\nAn alternative, the cancer stem cell hypothesis, places heterogeneity within a hierarchy. In this view only a small fraction of cells can drive tumor progression and are inherently therapy-resistant. Most current interpretations combine the two. Rather than mutually exclusive, branched Darwinian evolution integrated with a CSC hierarchy is considered a plausible explanation for intratumour heterogeneity, and recent breast cancer data favour branching and punctuated evolution driven by genome instability as well as nongenetic sources of heterogeneity.\n\nHeterogeneity has direct clinical consequences. Under therapy, cancer cells with greater adaptability are preferentially allowed to proliferate after treatment, while the majority of less adaptable mutant cells are eliminated. High intratumour heterogeneity is linked to aggressive disease and treatment resistance, worsening prognosis. In a 2009 study, sequencing of a primary tumour and its metastases from one patient showed that the mutational makeup of metastases diverged significantly from the primary tumor, suggesting that clonal selection occurs during disease progression.\n\nInvasion and the tumour microenvironment\n\nNormal ducts and lobules are enclosed by a basement membrane and a surrounding myoepithelial layer. Invasion requires cancer cells to breach these barriers, which involves matrix-degrading enzymes, loss of cell–cell adhesion and changes in cell shape and motility. Epithelial–mesenchymal transition and wider cellular plasticity are important in this process. A major focus is given to the role of EMT and cell plasticity in generating intratumoural heterogeneity and the varying contributions to tumour cell invasion, metastasis formation and the development of therapy resistance.\n\nThe surrounding stroma is not passive. Cancer-associated fibroblasts, tumour-associated macrophages, lymphocytes and inflammatory mediators all shape growth, local invasion and immune escape. The microenvironment also contributes to cellular diversity within a tumour; clonal evolution, cancer stem cells, and the tumor microenvironment drive diverse tumor cell populations. Immune infiltration and its interaction with tumour cells therefore influence both progression and the response to treatment.\n\nRoutes of spread and sites of metastasis\n\nCancer cells leave the primary tumour through lymphatic and blood vessels. Lymphatic spread usually reaches the regional lymph nodes first, most often in the axilla, and from there cells can access the bloodstream. Haematogenous dissemination carries cells to distant organs. Breast cancer can spread to almost every place in the human body, most frequently metastasizing to lymph nodes, bones, lungs, liver and brain. Among patients with metastatic disease, 30–60% have lesions in the bone, 4–10% in the brain, 15–32% in the liver, and 21–32% in the lung.\n\nThe pattern of spread depends on tumour biology. Hormone receptor (HR)-positive breast cancers tend to metastasize to bone, whereas HER2-positive and triple-negative breast cancers (TNBC) are more prone to visceral metastases such as liver, lung, or brain. Two early hypotheses explain this organ selectivity. In 1889 Stephen Paget proposed a \"seed and soil\" model, in which tumour cells grow preferentially in organs whose microenvironment is permissive. In the early 1900s, James Ewing suggested a competing theory that organ-specific metastasis was regulated solely by physiological blood flow patterns. Certainly the physical characteristics of organs such as the lung lends weight to Ewing's theory, particularly for breast cancer. Modern work suggests both mechanisms contribute, with the microenvironment of the target organ and the tumour cell's own molecular programme both mattering."
    },
    {
      "heading": "Histological types and non-invasive lesions",
      "text": "Most invasive breast cancers are sorted by their microscopic architecture. The largest group is invasive ductal carcinoma of no special type (NOS), a label applied to the great majority of tumours that do not match a recognised special type Breast carcinomas of \"special-types\" have been delineated based on their microscopical characteristics, but the vast majority of tumors belongs to the category of not otherwise specified (NOS) ductal carcinomas. Special types matter because they often carry distinct imaging appearances, behaviour and prognosis.\n\nInvasive ductal and lobular carcinoma\n\nInvasive lobular carcinoma (ILC) is the most common special type, accounting for 5%–15% of all invasive breast cancers (BCs) and is the second most common type of BC behind invasive ductal carcinoma (IDC) of no special type. Its biology is driven by loss of E-cadherin, a cell-adhesion protein. Without it, cells lose cohesion and infiltrate in single-file strands, and most tumours are oestrogen receptor-positive Distinctive biological hallmarks of invasive lobular carcinoma include the loss of cell adhesion molecule E-cadherin leading to cells with a discohesive morphology, proliferating into single-file strands and estrogen receptor positivity.\n\nThese features make ILC hard to find. Reported mammographic sensitivity is much lower, ranging between 57% and 81%, and false-negative rates exceed those for other invasive types A study by Krecke and Gisvold reported that the false-negative rate in the diagnosis of ILC is much higher than that for other invasive BCs. In histological series, lobular tumours also tend to spread diffusely through the breast, with extensive involvement in 65.4% of lobular cases compared with 45.7% of ductal cases Ductal cancers were extensive in 45.7% (268/586), lobular in 65.4% (87/133) of the cases. Certain germline variants, including in CDH1, show a stronger association with lobular histology several variants in ATM, BRCA2, CDH1, CHEK2, EPCAM, PALB2, and PMS2 are more strongly associated with ILC - to varying degrees.\n\nPrognostic findings are not uniform. An older Finnish cohort reported that lobular cancers had better long-term survival than ductal cancers The 5- and 30-year corrected survival rates of women with ILC were 78% and 50%, respectively, compared with 63% and 37% for women with IDC. A later analysis of oestrogen receptor-positive, HER2-negative tumours treated with chemotherapy found worse survival for lobular cancers, which suggests reduced chemosensitivity, and it argued that treatment recommendations should be considered separately for the two types Results from the analysis show worse survival in patients with ER+HER2− ILC after chemotherapy compared to ER+HER2− IDC, even after correcting for tumour size, grade, age, and nodal involvement at presentation, suggesting a worse response to chemotherapy in ILC. Thus, recommendations for chemotherapy treatment should be considered separately for the two subtypes.\n\nDuctal and lobular carcinoma in situ\n\nDuctal carcinoma in situ (DCIS) and lobular carcinoma in situ (LCIS) are both confined within the basement membrane, which distinguishes them from invasive disease Histopathologically, lobular carcinoma in situ (LCIS) and ductal carcinoma in situ (DCIS) are differentiated from invasive carcinoma by the confinement of malignant cells to the basement membrane. For a long time both were regarded as obligate precursors of invasive cancer, and prophylactic mastectomy was once advised for LCIS. Genomic and transcriptomic studies have since shifted this view, and both are now seen as non-obligate precursors along a spectrum of malignant progression recent genomic and transcriptomic analyses indicate molecular similarities in in situ and invasive cancers within the context of histologic grade as opposed to stage of progression. Current practice treats DCIS as a precursor, and LCIS as a marker of risk, although both are associated with invasive progression, including in the contralateral breast Currently, DCIS is treated as a precursor to invasive cancer, and LCIS as a risk factor for invasive cancer. However, evidence supports that both confer risk of invasive progression, including increased breast cancer risk to the contralateral breast.\n\nThe natural history of DCIS is uncertain because it cannot be followed directly The natural history of DCIS is poorly understood, as it cannot be observed directly.. The most direct evidence comes from women whose lesions were misjudged as benign and treated by biopsy alone, which suggests that between 14–53% of DCIS may progress to invasive cancer over a period of 10 or more years. Screening has changed how DCIS is found; it accounts for about 20% of all tumours diagnosed within mammographic screening programs. Regression is uncommon, and a systematic review of simulation models reported <10% of DCIS regress and there is no regression of invasive breast cancer. Higher grade is associated with a greater chance of progression and a lower chance of regression The grades of DCIS described the progression potential of DCIS, with high-grade having a higher probability of progression and a lower possibility of regression.\n\nPaget disease of the nipple\n\nPaget disease of the breast is a rare malignancy of the nipple–areola complex, accounts for approximately 1%–4% of all primary breast malignancies. Histologically it is an intraepidermal spread of malignant glandular cells in that region Histologically, it is characterized by an intraepidermal proliferation of malignant glandular epithelial cells in the nipple–areolar region.. Its early itching, scaling and redness can resemble eczema Early changes in PD include itching, scaling, and erythema of the nipple that can mimic other benign conditions, such as eczema.. Almost all cases coexist with an underlying carcinoma, although in one series Twelve to 15% of PDB cases are not associated with an underlying malignancy. Most cases show HER2 overexpression, reported at 84-91% of cases. Diagnosis rests on biopsy findings of Paget cells Diagnosis is usually made based on the histologic finding of Paget cells on biopsy.\n\nInflammatory breast cancer\n\nInflammatory breast cancer is a rare, aggressive subtype, accounting for 1% to 5% of breast cancer cases in women and almost none in men. Rather than forming a lump, it produces swelling, redness, skin thickening resembling orange peel, and sometimes nipple retraction Inflammatory breast cancer is characterized by swelling and redness in the breast, inverted or retracted nipple, and thickening or pitting of the breast skin that resembles orange peel, and may be itchy. Because it can be mistaken for mastitis, a breast infection that does not settle with antibiotics warrants consideration of this diagnosis Inflammatory breast cancer has a poor prognosis and should be a consideration in a patient with mastitis that does not resolve with appropriate antimicrobial therapy.\n\nAngiosarcoma\n\nAngiosarcoma arises from the endothelial cells of blood and lymphatic vessels and makes up Less than 1% of breast malignancies. Primary forms occur in women who have not had radiotherapy, usually in their 30s and 40s, whereas secondary forms develop in the irradiated breast, often within the last 8 to 10 years after treatment for earlier breast cancer. The 5-year survival for radiation-induced disease is 28% to 54%, and Mastectomy with negative margins is the standard treatment approach.\n\nClassification and treatment planning\n\nPathologists assign histological type, grade and in situ or invasive status from core biopsy or excision specimens. These categories shape the surgical and adjuvant pathway: invasive and in situ lesions are managed differently, lobular tumours may require supplementary imaging because they are harder to detect, and Paget disease requires the underlying lesion to be identified and characterised before treatment is planned."
    },
    {
      "heading": "Molecular subtypes and biomarkers",
      "text": "Hormone receptors and HER2\n\nClinical classification starts with immunohistochemistry on tumour tissue for oestrogen receptor (ER), progesterone receptor (PR) and HER2. A tumour is usually called hormone receptor-positive when a meaningful share of its nuclei stain for ER or PR, and a threshold of about 1% is commonly used to separate negative from low-positive results. Hormone receptor-positive tumours depend on hormone signalling and respond to endocrine therapy, whereas HER2 status marks tumours with overexpression or gene amplification of the receptor, which respond to HER2-directed antibodies. Together these three markers remain the first-line determinants of both likely biological behaviour and the choice of systemic treatment, and they are reported on every invasive carcinoma.\n\nIntrinsic molecular subtypes\n\nImmunohistochemistry groups tumours by a few proteins, whereas gene-expression profiling groups them by their overall transcriptional pattern. Microarray studies in the early 2000s used unsupervised hierarchical clustering to define intrinsic subtypes: luminal A, luminal B, HER2-enriched and basal-like, with a normal breast-like group also described. Luminal tumours are typically ER-positive and express luminal genes such as ESR1 and PGR, with luminal B tumours showing higher proliferation. HER2-enriched tumours show high expression of ERBB2 and neighbouring genes on the 17q amplicon, such as GRB7. Basal-like tumours are closest to triple-negative disease. The 50-gene PAM50 classifier, derived in 2009, allows subtype assignment from routine formalin-fixed paraffin-embedded blocks, and subtype has been shown to add independent prognostic information beyond standard clinicopathological variables. Subtypes are not interchangeable with their immunohistochemical surrogates, a point that matters for clinical decisions and for research comparisons. Subtype can also shift between a primary tumour and its metastasis: in a paired analysis of 123 patients, basal-like tumours kept their subtype in every case, whereas a large share of luminal A primaries were reclassified as luminal B in the metastasis.\n\nTriple-negative breast cancer\n\nTriple-negative breast cancer is defined by the absence of ER, PR and HER2 expression. Estimates of its share of cases vary between roughly 10% and 20%, depending on the study and the thresholds used. Its clinical course is generally more aggressive, with earlier age at onset and a higher early risk of relapse and death. In a Toronto cohort of 1,601 patients, the excess mortality was concentrated in the first five years after diagnosis. Triple-negative disease is also heterogeneous. Gene-expression analysis of 587 cases by Lehmann and colleagues identified six subtypes, including two basal-like groups, an immunomodulatory group, two mesenchymal groups and a luminal androgen receptor group, and these differ in survival: in one multicentre series, the basal-like immunosuppressed group had the poorest survival, while the luminal androgen receptor group had the best. Triple-negative status and basal-like status overlap substantially but are not synonymous, since a considerable share of triple-negative tumours fall outside the basal-like category. Some rare special histological types with a triple-negative phenotype, such as adenoid cystic carcinoma, follow an indolent course, and their recognition prevents unnecessary aggressive treatment.\n\nProliferation markers, genomic assays and emerging biomarkers\n\nThe Ki-67 index, the proportion of tumour cells staining for a nuclear proliferation antigen, is used to estimate growth rate and prognosis, particularly in ER-positive, HER2-negative early disease, where higher values are associated with a greater risk of death from breast cancer. Its clinical use is limited by inter-laboratory and inter-observer variability and by uncertainty over cut-off values; some guidance therefore applies it only at the extremes, such as values at or below 5% or at or above 30%. Multigene assays provide an alternative: the 21-gene Oncotype DX Recurrence Score was validated in hormone receptor-positive, HER2-negative invasive cancer to estimate distant recurrence and chemotherapy benefit, and other tests such as MammaPrint, Prosigna (PAM50), EndoPredict and CanAssist Breast are also in use. The correlation between Ki-67 and the Recurrence Score is only moderate, which is why the two should not be used interchangeably. Emerging markers under study include immune-related measures such as PD-L1 scoring, which guides the use of immune checkpoint inhibitors in selected triple-negative disease, along with tumour-infiltrating lymphocytes and circulating tumour DNA. Their predictive value for specific drugs is still being refined through clinical trials and correlative studies."
    },
    {
      "heading": "Clinical presentation and diagnosis",
      "text": "Many breast cancers are now found before any symptom appears. Many lumps are detected by a routine screening mammogram. A tumour that is still small is usually undetectable by touch or by sight, which is why imaging matters so much. When the tumor is small in the early stages of breast cancer, it's rarely noticeable to the touch or the naked eye. Among women who do notice a problem, a mass is the most common complaint, but it is not the only one. Skin and nipple changes form the other main group of presenting features, including swelling or shrinkage of all or part of the breast, dimpling, puckering of the skin, a nipple turned inward, breast or nipple pain, and discharge from the nipple, particularly if clear or bloody. In men, MBC most often presents with a palpable mass, while nipple discharge is rarer but may herald an underlying malignancy.\n\nSymptoms are not specific. Intraductal papillomas are a benign breast condition that can cause nipple discharge. Other conditions that can cause a lump in the breast and breast skin changes include breast cysts, breast infections (called mastitis), breast tissue changes caused by hormones or age and benign breast tumors. Discharge is judged by its pattern: signs of a more serious condition include discharge that occurs without squeezing the nipple, occurs in only one breast, or is bloody or clear (not milky). Scaling of the nipple also has a rarer explanation. Many patients do not visit the doctor because they assume Paget's disease of the breast to be minor contact dermatitis or eczema.\n\nImaging is the usual next step. Mammography, an X-ray examination of the breast, is supplemented by ultrasonography and magnetic resonance imaging, each with a different role. Mammography can show masses, calcifications and asymmetries, and the test results are scored in BI-RADS (Breast Imaging Reporting and Data System) categories, which range from category 1 (not cancer) to category 6 (high likelihood of cancer). Screening examinations use a narrower set, since for mammographic screening, BI-RADS categories of 0, 1 or 2 are given. For diagnostic imaging, BI-RADS categories 1–6 can be given. Ultrasound adds detail that mammography can miss and is most useful when mammography has already flagged something suspicious. MRI is less routine: breast MRI is generally recommended for high-risk women with dense breast tissue or when mammogram and ultrasound findings require further evaluation. Ultrasound and mammography also guide the needle during biopsy. Doctors use imaging techniques, such as ultrasound and mammography, to guide the placement of the needle.\n\nTissue diagnosis is decisive. Core needle biopsy is the standard and preferred way to diagnose breast cancer. A hollow needle removes cylinders of tissue, and the needle can be guided into the abnormal area by touch, if a lump can be felt, or by using an imaging test. Compared with fine-needle aspiration, which withdraws only cells or fluid, the core sample takes more time to examine than tissue removed via fine-needle aspiration, but it can potentially provide pathologists with more information. Sampling error is a real limitation: the needle can miss the tumor and take a sample of nearby normal tissue instead. For abnormal findings that can't be felt, false negative results occur in up to 4% of image-guided core needle biopsies. Surgical biopsy remains an option when the core result is unclear, since even if the tissue sample is benign, a surgical biopsy may be needed to rule out cancer. The pathologist then reports histological type, grade and receptor status. Adequacy of sampling is still debated: one core is sufficient for the diagnosis of invasive carcinomas, along with a reliable assessment of hormone receptor and HER2 status in many cases.\n\nImaging findings are triaged by category rather than read as yes or no. If the region of suspicion is classified as normal or benign, i.e., BI-RADS 1 or BI-RADS 2, then no further action may be taken. Category 3 means \"probably benign,\" with less than a 2% likelihood of malignancy. Such findings are followed up, with a 6-month follow-up to look for any changes. Categories 4 and 5 call for tissue, and within category 4 4C: 50% to just under 95% likelihood of being cancer. Category 5 carries a 95 percent chance or higher of being cancerous. These scores remain probabilistic, since the BI-RADS score is a statistic that is correlated with malignancy and not a deterministic measure of malignancy. Because most of these lumps have one thing in common: They're usually not cancerous tumors. The majority of lumps turn out to be harmless, or benign, masses or growths., the workup's central task is separating benign from malignant lesions, and tissue confirmation settles the question.\n\nThe axilla is assessed in the same spirit. Suspicious lymph nodes can be sampled under ultrasound guidance, and in a meta-analysis the accuracy of US-FNA in identifying suspicious axillary lymph nodes was as follows: overall sensitivity, 79%. In a single comparison, core biopsy detected six (8.6%) more cases of metastatic lymphadenopathy than FNA but the difference in sensitivities was not statistically significant."
    },
    {
      "heading": "Staging and prognostic assessment",
      "text": "The TNM framework and stage groups\n\nBreast cancer staging starts from the TNM system, which records the size of the primary tumour (T), the involvement of regional lymph nodes (N) and the presence of distant spread (M) separately before combining them. Stage ranges from 0 to 4, with stage 0 being pre-invasive disease (such as DCIS), and stage 4 being metastatic disease. Stages I to III describe locally or regionally confined disease of increasing extent. In broad terms, \"low stage\" cancers (Stages 0-II) tend to have better long term outcome than \"high stage\" cancers (Stages III-IV).\n\nThe eighth edition of the AJCC Cancer Staging Manual, published in 2017 and applied from 2018, added a second layer to the purely anatomical system. The anatomic stage is the traditional staging system defined by TNM categories. The prognostic stage is based on TNM categories and four biological factors: tumor grade, estrogen receptor (ER), progesterone receptor (PR), and HER2 status. The anatomic table remains useful where biomarkers cannot be routinely obtained, whereas the Prognostic Stage Group tables are preferred for patient care, and US cancer registries must use the prognostic table for reporting.\n\nClinical and pathological staging\n\nStaging is carried out in two phases. Staging done before surgery is called clinical prognostic staging, and staging done after surgery is called pathological prognostic staging. The clinical stage is assigned at diagnosis from history, examination, imaging and biopsy findings, and it is the stage used first for every patient. It must be determined before any systemic therapy begins. The pathological stage adds the findings from resected breast tissue and axillary nodes, together with the biomarker results, and the panel felt strongly supported by literature that this Pathologic Prognostic Stage Group is the most accurate predictor of outcome.\n\nNodal status is central to the pathological assessment. Sentinel lymph node biopsy allows the pathologist to report a nodal category from a small number of nodes rather than from a full axillary dissection; in the AJCC notation, a result such as \"pN0(sn)\" indicates that the sentinel nodes were negative. The surgical indications themselves are discussed in the surgical management section.\n\nClinical and pathological stages frequently differ. In one analysis of 433,514 patients, among individuals with stages I-III breast cancer not treated with neoadjuvant therapy, discordance between clinical and pathological staging occurred in 31.8% of patients, with upstaging in 8.7% and downstaging in 23.1%. Factors most highly associated with stage discordance were tumor grade, histology, and biomarker status. Lobular histology was also linked to upstaging. A single-institution Japanese series showed the same shift in distribution: stage IA made up 54.8% of anatomic stages but 66.6% of pathological prognostic stages. For a number of reasons, including limited complete pre- and post-therapy data on patients treated with neoadjuvant therapy, the AJCC panel did not create a separate post-neoadjuvant prognostic table, so for patients treated with neoadjuvant therapy staging depends on the clinical and post-treatment information available.\n\nGrade, biomarkers and prognostic performance\n\nHistological grade is one of the four biological inputs to the prognostic stage. Its value lies in the fact that it reflects how aggressive the tumour cells look under the microscope, and it is combined with ER, PR and HER2 status in the AJCC grouping. Validation studies have generally found the prognostic stage to be more informative than anatomy alone. In inflammatory breast cancer, one study found that incorporating biological factors into the traditional staging system provides more accurate inflammatory breast cancer (IBC) prognosis stratification than does the tumor size (T) and presence of lymph node involvement (N) and distant metastasis (M) (TNM) staging system. Reports from other institutions have not always agreed on the size of the stage shifts or on the survival gap between stages, so the degree of improvement is still debated.\n\nNomograms and recurrence-risk tools\n\nBeyond stage groups, prognostic tools estimate the individual risk of recurrence. Genomic assays play a role in node-negative, hormone receptor-positive, HER2-negative disease: in the AJCC 8th edition, if the OncotypeDx® test is performed in cases with a T1N0M0 or T2N0M0 cancer that is ER + /HER2-, the recurrence score (RS) is used to determine the pathological prognostic stage (ppStage).\n\nThe Clinical Treatment Score post-5 years (CTS5) addresses a different question: whether a woman still at risk after five years of endocrine therapy should continue treatment. The Clinical Treatment Score post-5 years (CTS5) was developed to estimate residual risk of late distant recurrence (DR) after 5 years of endocrine therapy. It integrates four clinicopathological variables to estimate the residual disease recurrence risk in hormone receptor-positive breast cancer patients who have been treated with five years of adjuvant endocrine therapy. In the ATAC cohort, the mean recurrence risk 5 to 10 years after completion of ET was 2.5% (95% CI, 1.8%─3.4%) in the low-risk subgroup, 7.7% (95% CI, 6.3%─9.5%) in intermediate-risk subgroup, and 20.3% (95% CI, 17.2%─24.0%) in high-risk subgroup. A meta-analysis reported a pooled hazard ratio of 5.41 (95% c.i. 4.50 to 6.51; P < 0.05) for the high-risk CTS5 category and 2.32 (95% c.i. 1.90-2.84; P < 0.05) for the intermediate category, relative to the low-risk group. On this basis, extended endocrine therapy may be unnecessary for patients with low CTS5 scores. Extended endocrine therapy should be offered for patients with intermediate or high CTS5 scores, especially those with high-ER and HER2− breast cancer.\n\nThe tools have limits. The CTS5 model does not accurately predict the risk of late recurrence in HR+, HER2+ breast cancer, particularly in patients treated with adjuvant trastuzumab. Some groups have therefore combined CTS5 and recurrence score into a single nomogram, and PR status has been reported as an independent predictor of late recurrence in the intermediate and high CTS5 groups. Decisions about adjuvant therapy, including the choice between chemotherapy and endocrine treatment, are ultimately made by weighing these estimates against the patient's tumour features and treatment toxicity."
    },
    {
      "heading": "Screening and early detection",
      "text": "Screening aims to find breast cancer in asymptomatic women, most often with mammography. The evidence that screening lowers breast cancer deaths rests mainly on randomised trials that began enrolling women three to four decades ago, and those trials used imaging and treatments that have since changed. A 2016 systematic review and meta-analysis prepared for the US Preventive Services Task Force reported a relative risk of breast cancer death of 0.92 for women aged 39 to 49, a result whose confidence interval crossed 1. For women aged 50 to 59 the figure was 0.86, which corresponded to about eight deaths prevented per 10,000 women over ten years. Reductions in advanced cancer were seen only from age 50. None of the trials showed a reduction in all-cause mortality. Observational studies have generally reported larger effects, but they are more vulnerable to bias.\n\nThe recommended starting age and interval differ across countries, reflecting different readings of the same data. Some bodies recommend annual mammography from age 40 for average-risk women, arguing that earlier detection gives smaller tumours, more surgical options and more effective chemotherapy. Other guidance favours biennial screening between about 50 and 74, on the grounds that the benefit for younger women is small in absolute terms while harms are relatively larger. Modelling studies have been used to compare these schedules; one set of estimates from the US Cancer Intervention and Surveillance Modeling Network projected a mortality reduction of about 42% for annual screening from 40 to 79, compared with about 25% for biennial screening from 50 to 74. These are model outputs rather than trial results, and the trials did not compare intervals directly. Screening interval and age-specific effects therefore remain partly inferred.\n\nScreening carries recognised harms. Recall for additional imaging leads to many false-positive results, and a proportion of women undergo benign biopsies. Supplemental screening with ultrasonography or magnetic resonance imaging in women with dense breasts increases false positives and benign biopsies without a clear demonstrated mortality benefit. Overdiagnosis is the most debated harm: some detected lesions, particularly ductal carcinoma in situ and other indolent tumours, would never have caused symptoms in a woman's lifetime, yet they can lead to treatment. Anxiety arising from callbacks and uncertain results is a less quantifiable cost.\n\nArtificial intelligence has been studied as a way to improve the reading of screening mammograms, either as a second reader or to triage cases. A randomised Swedish trial (MASAI) allocated over 100,000 women to AI-supported reading or standard double reading. The AI-supported arm was non-inferior for interval cancers, showed higher sensitivity at the same specificity of 98.5%, and reduced reading workload, with the additional detections mostly small, node-negative invasive cancers. A German observational implementation study of more than 460,000 women reported a detection rate of 6.7 per 1,000 with AI support against 5.7 per 1,000 without, and a slightly lower recall rate. Retrospective analyses of tomosynthesis screening found that an algorithm correctly localised about one third of interval cancers that had been missed at the time of screening, although cancers flagged by the algorithm were in some series larger and more often node-positive. Most published results measure detection, recall and interval-cancer rates rather than deaths, and performance varies across vendors, populations and reading workflows.\n\nIn low- and middle-income countries, population screening programmes are often absent or unorganised, with coverage that is uneven and largely opportunistic. Mammography requires equipment, maintenance, radiologists and pathology services that are scarce, and its costs are hard to justify in settings with limited health budgets and a high competing disease burden. For this reason, clinical breast examination and awareness programmes are frequently proposed as more feasible alternatives, though their effect on mortality is less well established. One review estimated that fewer than one in ten women in these countries have access to regular screening. Barriers also include limited public awareness, fear and embarrassment, transport distances and out-of-pocket costs. Organising any programme depends on reliable population cancer registries, diagnostic follow-up and treatment capacity, because screening detects cancers that must then be treated."
    },
    {
      "heading": "Surgical management",
      "text": "Breast-conserving surgery, mastectomy and margins\n\nSurgery for localised disease aims to remove the tumour completely while keeping the breast where possible. The key question in breast-conserving surgery is whether the rim of tissue removed around the tumour contains cancer. UK practice has followed NICE guidance, which before 2018 required a 1 mm margin for invasive carcinoma and 2 mm for ductal carcinoma in situ (DCIS). The 2018 update adopted \"no ink on tumour\" as the standard for both invasive cancer and DCIS. Positive margins carry a real cost: pooled analyses of invasive cancer found that involved margins more than doubled the rate of ipsilateral breast tumour recurrence. Wider margins beyond the ink, however, have not been shown to help. A consensus panel found that going beyond no ink on tumour did not further reduce ipsilateral recurrence overall or in subsets with unfavourable features such as young age or lobular cancer.\n\nRe-excision remains common. Published estimates vary: one review states that up to 20% of patients require further surgery, either cavity re-excision or completion mastectomy, while another reports margin re-excision rates varying between 15–35%. Assessing margins is technically difficult, partly because fixation of the specimen may artefactually narrow the ex vivo margin. Mastectomy, which removes the whole breast, is used when breast-conserving surgery is unsuitable, for example with multifocal disease or extensive tumour relative to breast size, and when the patient chooses it.\n\nAxillary management\n\nAxillary status has long been a central determinant of surgical extent. Sentinel lymph node biopsy (SLNB) allows many patients to avoid the morbidity of a full axillary dissection. The ACOSOG Z0011 trial tested whether dissection could be omitted in a selected group: patients with clinically node-negative T1 or T2 tumours and one or two positive sentinel nodes, treated with breast-conserving therapy, were randomised to completion axillary dissection or no dissection. Its results showed no difference in locoregional recurrence or survival between the two groups after a median follow-up of 6 years. Dissection did carry more harm: it produced more wound infections, axillary seromas and paraesthesias than SLNB alone, and lymphoedema was more frequent, though the difference was significant only by subjective report. Z0011 has since reshaped practice. Studies have shown a significant decrease in completion axillary dissection rates since Z0011.\n\nEligibility remains a practical issue. Axillary dissection is still required for patients with nodal disease found on a preoperative needle biopsy. In one institutional series, 73% of 51 patients with a positive needle biopsy had more than two positive nodes at dissection, while at least one-quarter had fewer than three positive nodes and potentially could have been treated with SNB alone. Features such as lymphovascular invasion and extranodal extension were associated with high-volume axillary disease. Patients who were underrepresented in Z0011 have been studied retrospectively, with high rates of locoregional control and disease-free survival, suggesting that completion dissection may be safely omitted in this population, though larger data sets and longer follow-up are needed.\n\nBreast reconstruction\n\nReconstruction can be performed immediately, during the mastectomy, or delayed until later. Options include implants and autologous tissue flaps, and the choice depends on the patient's body habitus, preferences and whether radiotherapy is planned, since radiation can increase complications in reconstructed breasts, particularly those with implants. Reconstruction is therefore usually planned jointly by the surgical, plastic and oncology teams. Skin-sparing mastectomy developed partly to conserve skin and facilitate breast reconstruction. Autologous techniques are not new: in the early 1900s, several European surgeons developed novel techniques for breast reconstruction using autologous tissue.\n\nHistorical development\n\nModern breast surgery grew out of the radical mastectomy. In 1882, William Halsted documented the first interventions he carried out, establishing guidelines in radical cancer surgery. His 1894 report recommended en bloc resection of all suspected tissues, including the pectoralis major muscle. The operation removed the breast, muscles and axillary lymph nodes, reflecting the belief that breast cancer spread locally at first, invading nearby tissue and then spreading to surrounding lymph ducts. Its results were regarded as exceptional, and the Halsted operation was performed on more than 90% of patients with breast cancer in the US until the 1970s. Attempts to make it more extensive were associated with significant morbidity and proved to be of little therapeutic benefit. By 1912, Murphy had abandoned the Halsted radical mastectomy in favour of preserving both pectoral muscles. Later steps followed in sequence: modified radical mastectomy, breast-conserving surgery, and then sentinel lymph node mapping, introduced with the hope of reducing the extent of axillary dissection. Together these changes moved surgery from removing whole regions towards removing only what the disease requires."
    },
    {
      "heading": "Radiotherapy and local control",
      "text": "Radiotherapy after surgery is the main tool for controlling disease in the breast and chest wall, and most trial evidence measures its value by how much it reduces local and regional relapse. For whole-breast irradiation after breast-conserving surgery, a pooled analysis of 17 randomised trials in 10,801 women by the Early Breast Cancer Trialists' Collaborative Group (EBCTCG) found that about 65% relative risk reduction in local recurrence at 10 years. The same analysis reported that radiotherapy lowered the 10-year risk of any first recurrence from 35.0% to 19.3%, and reduced 15-year breast cancer death from 25.2% to 21.4%.\n\nPost-mastectomy radiotherapy (PMRT) to the chest wall and regional nodes is used when the risk of recurrence is higher. The EBCTCG's 2014 individual-patient analysis of 8,135 women in 22 trials found benefit in node-positive disease. For patients with one positive node, 10-year local recurrence fell from 20% to 4%. A later analysis of 14,324 women in 16 trials of regional nodal irradiation found that the benefit was seen in more recent trials but not in older ones, which is attributed to differences in systemic therapy and techniques.\n\nFractionation has been a major area of change. Moderate hypofractionation, using 15 to 16 fractions of 2.6 to 2.7 Gy, is accepted in many countries as the standard for whole-breast treatment. The FAST-Forward trial tested a far shorter course: a single week of 26 Gy in five fractions was non-inferior for local control compared with 40 Gy in 15 fractions. Five-year ipsilateral breast tumour relapse was 2.1% after 40 Gy and 1.4% after 26 Gy. Late normal-tissue effects were more frequent with the 27 Gy schedule, while the 26 Gy schedule showed no statistically significant excess. Follow-up data suggest that late effects with the 26 Gy schedule were worse than the standard arm for most items as time passed. The schedule has been incorporated into UK guidance for breast, partial breast and chest wall irradiation. A review of the same data argues that moderate hypofractionation remains the standard for most patients, so the evidence on ultra-short courses is interpreted differently by different groups. Evidence for hypofractionated PMRT is much thinner: in FAST-Forward, only 264 patients had a mastectomy, and the trial reported too few events to draw firm conclusions.\n\nPartial-breast irradiation, which treats only the tumour bed, has been compared with whole-breast treatment in trials of selected low-risk patients. One such randomised comparison of accelerated partial breast irradiation by interstitial brachytherapy with whole-breast irradiation plus boost has reported 5-year results.\n\nOmitting radiotherapy has also been tested in carefully selected patients. The PRIME II trial randomised women aged 65 and over with small, node-negative, oestrogen receptor-positive tumours after breast-conserving surgery to whole-breast irradiation plus endocrine therapy, or endocrine therapy alone. At 10 years, the cumulative local recurrence rate was 9.5% without radiotherapy and 0.9% with it. Distant recurrence and overall survival did not differ between arms. The authors' conclusion depended on continued endocrine therapy: in a time-dependent analysis, women who stopped endocrine therapy had a higher local recurrence risk without radiotherapy. The CALGB 9343 trial reached a similar conclusion in low-risk elderly patients, and newer studies are testing genomic assays to identify who can safely avoid radiotherapy; one such phase II study uses a 50-gene transcriptional profile to define eligibility."
    },
    {
      "heading": "Systemic therapy",
      "text": "Endocrine therapy\n\nMost breast cancers express oestrogen receptors, so blocking oestrogen signalling is the mainstay of treatment for hormone receptor-positive disease. Tamoxifen, a selective oestrogen receptor modulator, has been the reference drug: in early ER-positive disease it cuts breast cancer death at 15 years by about a third. For women with early-stage oestrogen receptor (ER)-positive breast cancer, adjuvant tamoxifen reduces 15-year breast cancer mortality by a third. Aromatase inhibitors work by a different route, shutting down the enzyme that converts androgens into oestrogen, and they are preferred after menopause. In postmenopausal women, switching from tamoxifen to an aromatase inhibitor yields a further relative reduction in recurrence of about 30%.\n\nIn premenopausal women the ovaries remain a source of oestrogen, which limits what aromatase inhibitors can do alone. Without ovarian suppression, these drugs fail to help premenopausal women. Ovarian function suppression (OFS) is therefore added. It can be achieved with gonadotropin-releasing hormone agonists such as goserelin, triptorelin or leuprorelin, which suppress pituitary release of follicle-stimulating hormone and luteinizing hormone, and thereby oestradiol production. Surgical oophorectomy achieves the same effect permanently. In the SOFT trial, adding OFS to tamoxifen reduced distant recurrence and death, and combining OFS with an aromatase inhibitor gave larger absolute benefits than tamoxifen alone. Benefits of AI plus OFS versus tamoxifen alone were greater, with 3.0% and 2.6% absolute reductions in distant recurrence and death, respectively. For high-risk premenopausal patients with HER2-negative disease, dual endocrine therapy with OFS and an aromatase inhibitor is generally regarded as the optimal option. OFS brings adverse cardiometabolic effects, and in one meta-analysis hypertension was more frequent when OFS was added to tamoxifen.\n\nHER2-targeted therapy\n\nAnti-HER2 agents now comprise several classes. The first was trastuzumab, a monoclonal antibody approved in 1998, and the subsequent decades brought more than eight further products. Anti-HER2 therapies include monoclonal antibodies such as trastuzumab, pertuzumab and margetuximab, alongside tyrosine kinase inhibitors. Dual blockade with trastuzumab and pertuzumab, combined with a taxane, has produced survival beyond 57 months in first-line metastatic patients.\n\nAntibody–drug conjugates (ADCs) form the newest HER2 class. Trastuzumab emtansine (T-DM1), approved in 2013, links the antibody to a cytotoxic agent through a non-cleavable linker. Trastuzumab deruxtecan (T-DXd) is a second-generation ADC with a cleavable linker and a topoisomerase I inhibitor payload. Its drug-to-antibody ratio of 8:1 is much higher than that of earlier ADCs, which increases its cytotoxicity against heterogeneous tumours. Because the released payload can diffuse into neighbouring cells, T-DXd kills cells with low HER2 expression, a feature that makes it advantageous in diffuse metastatic disease. Its approval was extended to HER2-low metastatic breast cancer in 2022.\n\nChemotherapy\n\nCytotoxic chemotherapy remains part of treatment for many patients, particularly those with aggressive or endocrine-resistant disease. Its role has narrowed in hormone receptor-positive cases as endocrine and targeted options have expanded. In one institutional series of premenopausal lobular cancers, adjuvant chemotherapy use in stage II disease significantly decreased from 67% to 19% between 1990 and 2021. In triple-negative disease, which lacks all three receptor targets, chemotherapy is the backbone of systemic treatment, and it is combined with immune checkpoint inhibitors such as the PD-1 antibody pembrolizumab in selected early and metastatic cases, with eligibility depending on stage and PD-L1 expression. Antibody–drug conjugates targeting TROP2, such as sacituzumab govitecan, are also used in metastatic triple-negative disease after prior therapy.\n\nNewer agents\n\nThe CDK4/6 inhibitors have changed the management of hormone receptor-positive, HER2-negative disease. Three CDK4/6 inhibitors are approved to treat breast cancer: palbociclib, ribociclib and abemaciclib. They act by blocking Rb phosphorylation, which induces G1-phase arrest. In advanced disease, adding these drugs to endocrine treatment profoundly improved progression-free and overall survival. The use of these agents has extended to the adjuvant setting: in monarchE, abemaciclib with endocrine therapy reduced recurrence risk by one-third compared to endocrine therapy alone. Ribociclib in the NATALEE study showed a ~25% lower recurrence rate over a follow-up that remains short.\n\nPARP inhibitors target tumours with defects in DNA repair. In germline BRCA carriers with high-risk early disease, the OlympiA trial found that 1 year of the PARP inhibitor olaparib improved invasive disease-free and overall survival. In advanced hormone receptor-positive, HER2-negative disease, guidelines recommend PARP inhibitor monotherapy in the second-line setting for germline BRCA carriers after progression on a CDK4/6 inhibitor plus endocrine therapy. International guidelines recommend PARPi monotherapy in the second-line setting for patients with HR+/HER2− advanced breast cancer and germline BRCA LP/PVs, upon tumor progression to first-line CDK4/6i plus ET."
    },
    {
      "heading": "Multidisciplinary care and the evidence base",
      "text": "Team-based management\n\nBreast cancer care is organised around a team rather than a single specialist. In breast cancer surgery, multidisciplinary teams (MDTs) typically include surgeons, medical oncologists, radiation oncologists, radiologists, and pathologists. The pathologist's role extends beyond the initial report. Central pathology review of each case by an expert pathologist before the multidisciplinary meeting provides the opportunity to re-evaluate diagnoses and to identify any discrepancies that may influence management. Meeting attendance varies by setting. In a survey of teams in 39 countries, medical oncologists and surgical oncologists attended in about 95% of meetings, radiation oncologists in 90%, pathologists in 84% and radiologists in 73%. Most (90%) respondents from Europe stated that their MDTs met weekly, compared with only half (50%) of the respondents from Asia. Team discussion is the forum in which surgical, systemic and radiation options are sequenced for an individual patient.\n\nAdjuvant therapy\n\nAdjuvant therapy is treatment given after local surgery to reduce the risk of microscopic disease that has spread but cannot be detected by conventional diagnosis. The concept rests on the view that breast cancer is systemic from an early stage. Treatment of breast cancer for the last 40 years has been based on the hypothesis that this malignancy is systemic at time of diagnosis. The benefit is estimated from pooled data. The Early Breast Cancer Trialists' Collaborative Group, established in 1985 to coordinate individual-patient-level meta-analyses of all randomised trials of adjuvant treatments, has quantified the effects of several modalities. In an overview of polychemotherapy, recurrence fell by 35% among women under 50 and by 20% among those aged 50 to 69, and the recurrence reductions emerged chiefly during the first 5 years of follow-up, whereas the difference in survival grew throughout the first 10 years. For tamoxifen, the proportional recurrence reduction over about 10 years of follow-up was 47% (SD 3) in trials of about five years of treatment. The absolute benefit depends on the starting risk. The absolute risk reductions produced by tamoxifen depend on the absolute breast cancer risks (after any chemotherapy) without tamoxifen.\n\nEach benefit must be weighed against toxicity. Anthracycline and taxane chemotherapy can cause myelosuppression, neuropathy and cardiac effects; tamoxifen carries a risk of thromboembolism and endometrial changes; aromatase inhibitors are associated with bone loss and joint symptoms; and ovarian function suppression induces menopausal symptoms. Because a patient with low absolute risk may gain little from a treatment with substantial side effects, the decision is individualised rather than applied uniformly.\n\nLandmark randomised trials\n\nThe National Surgical Adjuvant Breast and Bowel Project (NSABP), chaired by Bernard Fisher, produced many of the trials that shaped modern practice. Its early work tested adjuvant chemotherapy. Single agent chemotherapy was used (thio‐TEPA), at a time when the most effective agents and combination therapy were not yet available. In addition, the trials included relatively modest numbers of patients and were thus hopelessly underpowered. Protocol B-04 compared radical with total mastectomy, and radical mastectomy provided no survival advantage for breast cancer patients when compared with simple mastectomy. Protocol B-06, begun in 1976, tested breast-conserving treatment. The NSABP-B06 trial showed equivalent outcomes from total mastectomy versus breast conserving surgery (BCS) with adjuvant radiotherapy (RT). The trial also showed that BCS without RT was associated with a high locoregional recurrence rate which eventually translated into a survival disadvantage. Later trials of tamoxifen, including B-14, established its value in patients whose tumors contained estrogen receptors. Because the B-06 trial was conducted in the era of mastectomy, its conclusions were contested for some years, and the equivalence of breast conservation was confirmed only after longer follow-up.\n\nClinical trials and consent\n\nNew systemic and radiotherapy approaches are generally introduced through phased clinical trials, usually a randomised comparison against the current standard. Randomisation is considered ethically acceptable when clinicians are genuinely uncertain which arm is better, a principle often described as equipoise. Participation requires informed consent, which in principle means that a patient understands the purpose, procedures, alternatives, risks and the right to withdraw without losing standard care. Oversight is provided by ethics committees and institutional review boards, and consent is treated as an ongoing process rather than a single signature. Trial populations have historically under-represented older women and some ethnic groups, which raises questions about how far results apply to the wider patient population. These ethical concerns are central to the ethics of research and to the design of trials that test de-escalation of treatment in low-risk disease."
    },
    {
      "heading": "Metastatic disease and survival",
      "text": "Stage IV disease means that the cancer has spread beyond the breast and regional lymph nodes to distant organs, a process called metastasis. Metastatic disease is the main cause of death from breast cancer. Even with modern treatment, the 5-year survival rate of patients with metastatic breast cancer has been reported at less than 30%. Because most patients who die from the disease have spread that was not controlled by earlier treatment, the biology of metastasis is a central concern of cancer research.\n\nBone is the most frequent site of distant spread in most subtypes, although basal-like tumours are an exception. In a large US registry analysis, bone metastases were the most common, followed by liver, lung and brain. Visceral sites, especially the brain, are linked with poorer outcomes. In a SEER population analysis, patients with bone metastasis had the best survival, while those with brain metastasis had the shortest median overall survival, at about 11 months. Triple-negative and HER2-positive tumours tend to metastasise to the liver, lung and brain more often, and hormone receptor-positive tumours more often to bone. Survival also depends on how many organs are involved: in a Swedish cohort, involvement of three or more sites and age over 80 were independent predictors of death, whereas the time elapsed since the original diagnosis was not.\n\nSurvival differs markedly by biological subtype. In an early cohort of women with early-stage disease, median survival after distant spread ranged from about 2.2 years in luminal A tumours to about 0.5 years in basal-like tumours. In a more recent Swedish cohort, 5-year survival was highest for HER2-positive luminal tumours (46%) and lowest for triple-negative disease (7%), and the median overall survival of all 370 patients was 32.5 months. Patients who present with metastatic disease at first diagnosis (de novo) generally do somewhat better than those who relapse later, particularly when the disease-free interval before relapse is short. Patients whose relapse involves bone or lung have longer post-relapse survival than those with brain recurrence, and symptomatic presentation is consistently associated with poorer prognosis.\n\nTreatment goals in metastatic disease are generally not cure. Systemic therapy is the mainstay, and it aims to control the disease, relieve symptoms and preserve quality of life, with the balance between efficacy and toxicity guiding the choice of drugs. Local surgery is used selectively, and the value of aggressive locoregional treatment remains under study. Endocrine therapy is usually the first choice for hormone receptor-positive disease, and CDK4/6 inhibitors added to endocrine therapy have further improved outcomes in this group. Many patients also receive palliative and supportive care for bone-related complications and other symptoms.\n\nSurvival has improved over several decades. In a Swedish regional series, median survival rose from 13 months among patients diagnosed in 1985–1989 to 33 months among those diagnosed in 2011–2014, and 5-year survival rose from 10% to 27%. The most marked gain was seen in HER2-positive disease after trastuzumab became available in 2000, when median survival increased from about 14 months to 29 months. A German single-centre study reported similar gains over two decades, and a more recent cohort showed median overall survival rising from about 25 months to 49 months across three five-year periods, although progression-free survival did not improve significantly over the same period. Newer agents have added further benefit: in a 2025 trial, adding inavolisib to a CDK4/6 inhibitor and fulvestrant extended median overall survival from 27 to 34 months in PIK3CA-mutated, hormone receptor-positive disease. Gains have been smaller for triple-negative disease, where a US retrospective analysis found only a modest rise in 5-year survival after the introduction of PARP and immune checkpoint inhibitors, possibly because of limited access to these drugs. Longer survival also means that more patients live for extended periods with incurable disease, which increases the importance of quality of life and palliative care in long-term management."
    },
    {
      "heading": "Survivorship, quality of life and psychosocial care",
      "text": "Long-term physical effects of treatment\n\nSurvivorship care addresses effects that can last for years after active treatment ends. Lymph node surgery and radiotherapy are the main causes of lymphatic swelling in the arm. Estimates of lymphoedema in people with localised disease range from 14% to 40%, and although most cases appear within two years of treatment, some develop much later. With modern sentinel lymph node sampling procedures, estimated breast-cancer-associated lymphedema risk is lowered to 6–10%. Untreated swelling can lead to chronic inflammation, pain, reduced mobility and psychological strain, which in turn reduce the use of the affected limb (Untreated lymphedema causes chronic inflammation, cellulitis, pain, fatigue, cosmetic deformity, restriction in mobility and related problems).\n\nFatigue is one of the most frequent and persistent complaints. Causes of fatigue, sleep problems, cognitive changes and psychological concerns may be multifactorial and more than one of these issues often coexist. Clinicians therefore look for treatable contributors such as anaemia, thyroid disease and cardiac dysfunction. Structured exercise is one of the better-supported interventions: Exercise has also been associated with reductions in cancer-related fatigue, one of the most common and debilitating symptoms experienced after cancer treatment. Additional benefits include improvements in sleep quality, psychological wellbeing, and overall health-related quality of life.\n\nCardiotoxicity and endocrine effects\n\nSome chemotherapy and antibody treatments carry a risk to the heart. HER2‐targeted therapies were linked to cardiotoxicity, and radiotherapy has been associated with ischaemic heart disease. Anthracycline-based chemotherapy and trastuzumab are the regimens most often cited in discussions of cardiotoxicity. Because breast cancer and cardiovascular disease share risk factors such as age, excess body weight and low physical activity, cardiac monitoring is usually integrated into survivorship planning rather than treated as a separate issue.\n\nEndocrine therapy and ovarian suppression alter hormone levels and produce treatment-related menopause. Treatment‐related hormonal changes can induce menopausal symptoms, sexual dysfunction, and infertility, posing additional emotional and social burdens. Aromatase inhibitors are also associated with bone loss and joint pain, so bone density and musculoskeletal symptoms are routinely monitored.\n\nPsychological effects, body image and sexuality\n\nAnxiety, depression, posttraumatic stress, and persistent cancer‐related fatigue are prevalent among survivors, affecting overall well‐being and functional capacity. Concerns about anxiety and recurrence are often prominent, and fear of recurrence is increasingly treated as a clinical target rather than a normal reaction to diagnosis. Changes to the body after mastectomy, reconstruction or hormonal treatment can affect self-image, intimacy and sexual function, and these effects are often under-discussed in consultations. Support typically includes psychological counselling, cognitive behavioural therapy and referral to mental health services when depressive symptoms persist, with partners frequently included where appropriate.\n\nFertility, pregnancy and hereditary risk in younger women\n\nYounger women face distinct survivorship questions. In a multicentre prospective cohort of women diagnosed at age 40 or younger, most participants (73%) reported at least one pregnancy after diagnosis, and 65% reported at least one live birth. Chemotherapy can cause permanent ovarian failure, and below 40 years of age, the risk of permanent chemotherapy-induced ovarian function failure is approximately 20%. For this reason, fertility preservation is discussed before treatment starts. Oocyte and embryo cryopreservation should be offered as first-line options, with OTC and GnRHa as alternatives when standard methods are not feasible.\n\nEvidence on the safety of pregnancy has changed over time. Historically, clinicians advised delaying pregnancy for several years after breast cancer diagnosis, primarily out of concern for recurrence risk. Large-scale meta-analyses and pooled cohort studies have consistently shown that pregnancy after breast cancer does not worsen disease-free or overall survival. Observational data suggest better survival among women who conceive, but this is partly explained by the \"healthy mother effect\", in which women who become pregnant tend to have more favourable tumour biology. Practical rules still apply: tamoxifen is teratogenic, so women who are trying to conceive should discontinue tamoxifen for at least three months before attempting pregnancy. For women with a pathogenic variant in a hereditary cancer gene, pre-implantation genetic testing is also discussed, and referral to a combined breast, fertility and genetics service is recommended soon after diagnosis.\n\nPalliative care and supportive care\n\nThe WHO and the American Society of Clinical Oncology recommend that palliative care begin early in the course of advanced cancer rather than only at the end of life. Evidence for breast cancer specifically is smaller than for the cancers as a whole. In a Korean randomised trial of 144 patients with advanced cancer, those randomized to the EPC intervention group experienced better quality of life at 18 months, but not at 12 or 24 months, compared with the control group. A Belgian randomised trial reported improved quality of life with systematic early integration of palliative care alongside standard oncological treatment. A retrospective cohort of 200 women with advanced breast cancer found lower symptom burden and better sleep among those who received early integrated care, although its design limits causal inference. Feasibility problems also exist: a phase II trial in Melbourne found that recruitment was workable for brain cancer but enrolled only six patients with breast cancer against a target of 30.\n\nSupportive care is meant to run alongside disease-directed treatment rather than replace it. In practice, this means routine screening for symptoms, rehabilitation for lymphoedema and function, nutritional advice, and early referral for psychological or sexual health problems, so that these needs are identified during treatment and not only after it has ended."
    },
    {
      "heading": "Global health policy and health equity",
      "text": "The World Health Organization set up its Global Breast Cancer Initiative (GBCI) in March 2021 to bring together stakeholders across sectors. Its shared goal is reducing global breast cancer mortality by 2.5% per year, thereby averting 2.5 million breast cancer deaths globally by 2040. The programme is organised around three pillars and specific targets: at least 60% of invasive cancers diagnosed at stage I or II, evaluation completed within 60 days, and at least 80% of patients completing a full course of multimodality treatment. Progress against these benchmarks is uneven. In Ghana, for example, the timely diagnosis indicator was met, but early detection and treatment completion fell short.\n\nThe burden is concentrated where resources are weakest. In 2024 roughly 694,000 women died of breast cancer, and about 70% of those deaths occurred in low- and middle-income countries (approximately 694 000 deaths globally – 70% in low- and middle-income countries). Survival figures show the scale of the gap. The WHO's first global survival estimates place median five-year survival at 41.9% in low-income countries, against 87.3% in high-income countries (rising to 60.1% in lower-middle-income countries, 78.7% in upper-middle-income countries, and 87.3% in high-income countries). Earlier WHO figures give a similar picture at the national level, with five-year survival above 90% in high-income countries compared with about 66% in India and 40% in South Africa.\n\nLate presentation is a central mechanism. In high-income settings, more than 70% of patients are diagnosed at stage I or II, whereas in low- and middle-income countries an estimated 20–50% are diagnosed with advanced disease (it is estimated that more than 70% of breast cancer patients are diagnosed in the early stages of cancer [stage 1 or 2]). Where mammography is scarce, detection often depends on women noticing a lump, so an early diagnosis is hard to achieve. Financial barriers compound the problem. Case studies by the UICC-led Access to Oncology Medicines Coalition in the Philippines, Kenya, Zambia and Georgia link unaffordable care and limited access to medicines to late diagnoses and survival inequities. Diagnostic capacity is a further bottleneck, which is why the GBCI sets a 60-day limit for completing imaging, tissue sampling and pathology.\n\nUniversal health coverage is associated with better care, but it does not remove inequities on its own. An international comparison found that a higher universal coverage index tracked with better breast cancer care quality, and its authors argue for extending coverage explicitly to breast cancer services (expanding the universal health coverage with inclusion of breast cancer care may help improving the breast cancer care quality and reduce the disproportionate mortality). Brazil illustrates the limits. Although universal coverage through the Unified Health System (Sistema Único de Saúde [SUS]) exists, major inequities in access, timely diagnosis, and treatment persist when compared with the private sector. In that registry study, the five-year overall survival rate was 66.2% in the public system and 79.7% in private care. Between 1990 and 2020 only 20 high-income countries met the breast cancer mortality reduction targets, and the same period saw a 40% decline in breast cancer mortality over the past two decades in high-income countries, while LMICs have not experienced a similar reduction.\n\nSocial determinants shape outcomes even within universal systems. In a Swedish nationwide cohort of 473 women with breast sarcomas, lower household income, but not educational attainment, was associated with worse overall survival, even after adjustment for age and comorbidity. Researchers suggest that in publicly funded systems, such gaps can reflect the practical ability to access and engage with available care, including factors, such as taking time off work or managing childcare. In Colombia, although formally employed women benefit from universal health care coverage, significant income disparities persist, potentially affecting timely diagnosis, treatment access, and survival outcomes. In the United States, the cumulative impact of the key SES indicators income, education, and occupation results in substantial disparities in breast cancer treatment and long-term survival. Addressing these inequities therefore requires measures that reach beyond the health service itself, including attention to income, education and the practical conditions under which women can seek care."
    },
    {
      "heading": "Open questions and continuing debates",
      "text": "The age at which population screening should start and stop is still disputed. The US Preventive Services Task Force now recommends biennial screening from age 40 to 74, but it noted that no randomised trials had compared different start or stop ages for mortality or quality-of-life outcomes, so much of the guidance rests on modelling and observational data. One trial emulation using Medicare claims linked continued screening between 70 and 74 with a lower breast cancer mortality than stopping at 70. Overdiagnosis, meaning the detection of cancers that would never have caused harm, is hard to measure because it requires follow-up of screened and unscreened cohorts over decades. Some authors argue that start age and screening interval do not change how many overdiagnosed cancers exist, only when they are found, and that overdiagnosis therefore should not drive guideline design. Others give it more weight, so the disagreement concerns how benefits and harms are valued as much as the underlying data. Estimates of how many cancers found on mammography would never progress also vary considerably by age group, which keeps the question open.\n\nRisk-adapted treatment raises a parallel problem. Several landmark trials established that radiotherapy can be omitted after breast-conserving surgery in carefully selected low-risk women, including older patients with small hormone receptor-positive tumours. Single-arm studies such as LUMINA and IDEA then used gene-expression profiling and biomarkers to define even smaller low-risk groups with very low local recurrence rates. Randomised comparisons with longer follow-up, however, reported locoregional recurrence of around 10% without radiotherapy against roughly 1–2% with it, so low rates in highly selected single-arm cohorts do not settle the question. Justifying de-escalation therefore requires prospective randomised data with prespecified endpoints. Omitting one treatment can also shift risk elsewhere: omitting axillary surgery in node-positive disease has led to greater use of regional radiotherapy. A systematic review of locoregional de-escalation trials identified 97 studies, with considerable duplication of questions, and patient-reported acceptance is uneven. In one survey of older adults, a substantial minority were not comfortable with participating in de-escalation trials. Trials of reducing endocrine therapy itself are at an earlier stage.\n\nAccess to high-cost drugs forms a further debate. Breast cancer carries the highest treatment cost of any cancer in the United States, and the cost of monoclonal antibodies and other targeted agents has grown substantially. Analysts have argued that the high price of some HER2-directed regimens limits availability, particularly for underserved groups, and that prices in the United States are considerably higher than in comparable countries despite similar outcomes. Out-of-pocket costs can force patients to delay or forgo treatment, and in some low- and middle-income settings the regimens listed on national essential medicines lists have been found to be unaffordable for patients paying directly. In Latin America, patients with HER2-positive disease have been treated largely with older chemotherapy because anti-HER2 agents are not widely available. Because newer drugs are increasingly approved for biomarker-defined subgroups, the population eligible for each drug is smaller, which affects both per-patient prices and the evidence available for pricing decisions. How public coverage and drug development policies should be designed to reconcile innovation with equitable access remains unresolved.\n\nSeveral research gaps remain. Men account for a small share of cases, and treatment decisions for them are often extrapolated from trials conducted mainly in women, so trials specific to male patients are limited. Cancers in young women are also under-studied relative to their clinical significance; the biology, genetic background and treatment needs of premenopausal patients, including questions about pregnancy after treatment, need more prospective data. Finally, the environmental causes of breast cancer are still uncertain. Proposed exposures, including some chemicals, radiation and circadian disruption, have been studied with inconsistent results, and establishing causal links requires large epidemiological studies with careful exposure measurement."
    }
  ],
  "links": [
    "world-health-organization",
    "cancer",
    "cell",
    "mutation",
    "gene-expression",
    "genetics",
    "biopsy",
    "pathology",
    "surgery",
    "radiation-therapy",
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    "chemotherapy",
    "cancer-immunotherapy",
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    "dna",
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    "hormone",
    "x-ray",
    "ultrasonography",
    "magnetic-resonance-imaging",
    "biomarker",
    "lymph-node",
    "diagnosis",
    "informed-consent",
    "ethics",
    "quality-of-life",
    "palliative-care",
    "lymphatic-system",
    "lymphedema",
    "inflammation",
    "physical-therapy",
    "menopause",
    "anxiety-disorders",
    "psychotherapy",
    "cognitive-behavioral-therapy",
    "mental-health",
    "depression",
    "randomized-controlled-trial",
    "rehabilitation",
    "nutrition",
    "income-inequality",
    "universal-health-coverage",
    "pharmacology",
    "pregnancy",
    "epidemiology"
  ],
  "sources": [
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    {
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    {
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      "url": "https://www.ahdbonline.com/issues/2023/june-2023-vol-16-no-1/trends-in-utilization-prices-and-spending-for-oral-medications-for-breast-cancer-treatment-in-the-us-medicaid-population-2008-2019"
    },
    {
      "title": "Access to high-cost drugs for advanced breast cancer in Latin America, particularly trastuzumab",
      "url": "https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6372298/"
    },
    {
      "title": "Access to and Affordability of World Health Organization Essential Medicines for Cancer in Sub-Saharan Africa: Examples from Kenya, Rwanda, and Uganda",
      "url": "https://academic.oup.com/oncolo/article/27/11/958/6673082"
    },
    {
      "title": "Health and Economic Benefits of Breast Cancer Interventions",
      "url": "https://www.cdc.gov/nccdphp/priorities/breast-cancer.html"
    }
  ],
  "license": "https://creativecommons.org/licenses/by/4.0/"
}