Leukemia is a group of cancers arising in blood-forming tissues, principally the bone marrow. It involves the abnormal growth of blood-forming cells, commonly cells belonging to white blood cell lineages. These malignant cells can accumulate in marrow and blood, interfering with normal blood production. Leukemia comprises biologically distinct diseases rather than a single condition; its classification depends on the affected cellular lineage, the pace of progression, and molecular features. (cancer.gov)
Classification and major types
The traditional classification combines two distinctions. Acute leukemias develop rapidly and characteristically involve immature cells called blasts. Chronic leukemias generally progress more slowly and involve more mature-appearing cells. Lymphoid leukemias arise from lymphocyte lineages, whereas myeloid leukemias arise from other blood-forming lineages. These distinctions produce four major groups, each containing further subtypes. (cancer.org)
- Acute lymphoblastic leukemia (ALL) involves immature lymphoid cells, most often precursors of B cells or T cells. It is the most common childhood cancer, although it also occurs in adults. (cancer.gov)
- Acute myeloid leukemia (AML) involves abnormal myeloid precursors. Its subtypes differ in cellular appearance, genetic changes, clinical behavior, and treatment response. (cancer.gov)
- Chronic lymphocytic leukemia (CLL) usually involves abnormal B lymphocytes and predominantly affects adults. Some cases remain asymptomatic for long periods. (cancer.gov)
- Chronic myeloid leukemia (CML) is associated with the BCR::ABL1 fusion gene and commonly begins in a chronic phase, but can progress to a blast phase. (cancer.gov)
Less common forms include hairy cell leukemia and other specialized entities. Cellular lineage and genetic findings therefore provide information beyond the broad acute–chronic division. (cancer.gov)
Biological basis and risk factors
Normal hematopoiesis produces red blood cells, white blood cells, and platelets from blood-forming stem cells. Leukemia disrupts this process through genetic alterations affecting cell growth, maturation, or survival. Changes in DNA, including mutations and rearrangements of chromosomes, can alter the activity of genes that regulate these functions. (cancer.gov)
CML provides a well-characterized example. An exchange of material between chromosomes 9 and 22 creates the Philadelphia chromosome, which carries BCR::ABL1. The resulting abnormal protein promotes uncontrolled growth of blood-forming cells. This alteration is acquired rather than passed from parent to child. It also occurs in some acute leukemias. (cancer.gov)
Risk factors vary by subtype. For AML, established associations include older age, smoking, benzene exposure, radiation exposure, previous treatment with certain anticancer drugs, and some inherited syndromes or preceding blood disorders. A risk factor increases the likelihood of disease but does not establish the cause of an individual case; many affected people have no recognized risk factors. (cancer.gov)
Clinical features
Many manifestations result from impaired normal blood production. Reduced red blood cell production can cause fatigue, pallor, and breathlessness. Reduced platelets can produce easy bruising or bleeding. Deficient or dysfunctional infection-fighting cells can increase susceptibility to infection, even when the total white blood cell count is elevated. (cancer.gov)
Other manifestations include fever, night sweats, weight loss, bone pain, and enlargement of lymph nodes or the spleen. Their frequency depends on the leukemia subtype. Acute forms commonly become symptomatic over a relatively short interval, whereas chronic forms may be discovered during blood tests performed for unrelated reasons. These features are not specific to leukemia. (medlineplus.gov)
Diagnosis and characterization
Diagnosis combines clinical findings with laboratory examination. A complete blood count measures blood cell numbers, while examination of a blood smear assesses cellular appearance. Bone marrow aspiration and biopsy provide samples for evaluating abnormal cells and the state of normal blood formation; the required investigations differ among subtypes. (medlineplus.gov)
Flow cytometry identifies characteristic cellular markers and helps establish lineage. Cytogenetic and molecular tests identify chromosome abnormalities, gene fusions, and mutations. These findings can distinguish subtypes, inform prognosis, and identify treatment targets. In selected circumstances, cerebrospinal fluid examination evaluates involvement of the central nervous system. (cancer.gov)
Treatment
Treatment varies substantially with subtype, genetic findings, age, general health, and previous response. Chemotherapy remains an important component of treatment for acute leukemias. Treatment commonly includes an induction phase intended to achieve remission, followed by additional therapy to reduce recurrence; ALL generally also includes maintenance and central nervous system–directed treatment. (cancer.gov)
Targeted drugs interfere with specific processes supporting malignant cells. CML treatment prominently uses inhibitors of BCR::ABL1 activity. CLL therapies include inhibitors of cellular signaling or survival pathways and monoclonal antibodies. Asymptomatic CLL may be managed initially with structured observation rather than immediate treatment. (cancer.gov)
Cancer immunotherapy, including CAR T-cell therapy, is used for selected leukemias. Hematopoietic stem cell transplantation is another option in defined circumstances. Radiation therapy has more limited, specific roles. Supportive care can include transfusions and treatment of infections. (cancer.gov)
Prognosis and response assessment
Prognosis depends on the specific disease, genetic characteristics, age, health status, and depth of treatment response. Remission denotes a substantial reduction or disappearance of detectable disease, but is not necessarily equivalent to cure. Sensitive tests can detect measurable residual disease that remains below the threshold of routine microscopy. In ALL, residual disease measurements are important for assessing relapse risk and assigning treatment intensity. (cancer.gov)