Pathology is the scientific study of disease and a medical specialty concerned with identifying and explaining abnormalities in tissues, cells, and body fluids. It connects laboratory science with clinical medicine, providing evidence for diagnosis, disease classification, treatment planning, and monitoring. Its scope includes both research into disease mechanisms and the examination of specimens from individual patients. Although associated in public understanding with postmortem examination, much of pathology concerns diseases in living people. (rcpath.org)
Scope and conceptual framework
Pathology investigates how disease develops and how its effects can be recognized. Important distinctions include etiology, the cause of a disease; pathogenesis, the sequence of processes through which it develops; and the structural and functional abnormalities that result. These dimensions are related but not interchangeable: a shared cause can produce different diseases, while similar tissue abnormalities can arise through different mechanisms. Clinical–pathological correlation connects laboratory observations with a patient’s symptoms and other findings. (pmc.ncbi.nlm.nih.gov)
The discipline operates at several scales, from whole organs to individual cells and molecular changes. Examination of tissue architecture remains central, while genetics and molecular biology supply additional ways to characterize disease. Pathology therefore encompasses more than recognizing abnormalities under a microscope: it also involves selecting laboratory investigations, interpreting their results, and relating those results to clinical information. (rcpath.org)
Principal branches
In the United States, professional practice commonly distinguishes anatomic pathology from clinical pathology, although their responsibilities overlap. Anatomic pathology examines organs, tissues, and cells. It includes surgical pathology, which studies specimens obtained through biopsy or surgery, and cytopathology, which evaluates cells collected through sampling procedures or present in body fluids. Postmortem examination is another component. (documents.cap.org)
Clinical pathology, also called laboratory medicine, covers the examination of blood and other specimens using chemical, cellular, microbiological, and molecular methods. Its fields include clinical biochemistry, blood-related investigations, microbiology, and transfusion medicine. The organization of these specialties differs between countries; in some systems, several are distinct clinical disciplines within a broader pathology service. (documents.cap.org)
Specialization may also follow an organ system, specimen type, or diagnostic technique. Examples include neuropathology, dermatopathology, and molecular pathology. Forensic pathology concerns the investigation of deaths with legal significance, particularly unnatural deaths. It is a specialized part of pathology rather than a description of the entire profession. (rcpath.org)
Specimen examination and laboratory methods
In histopathology, tissue is first assessed macroscopically for features such as size, appearance, and visible abnormalities. Selected portions are commonly fixed in formalin, embedded in paraffin wax, cut into thin sections, and stained for microscopic examination. These preparations preserve tissue detail and can be retained for further investigation. Frozen sections provide a more rapid examination when an answer is needed during an operation, but generally preserve less structural detail than permanent sections. (cancer.gov)
Additional methods address questions that routine examination cannot resolve alone. Immunohistochemistry detects proteins in tissue or cell preparations using antibodies directed against particular targets. The distribution of staining can help characterize a lesion and contribute to diagnosis, prognosis, or treatment-related testing. Such results are interpreted alongside other pathological findings rather than independently of them. (ccr.cancer.gov)
Molecular investigations examine characteristics such as the structure and sequence of DNA. In tumor pathology, these findings can refine disease classification and identify clinically relevant differences between tumors that appear similar microscopically. Clinical laboratory methods extend beyond tissue examination, ranging from routine measurements in blood to molecular tests and genome sequencing. (cancer.gov)
Diagnostic interpretation and reporting
A pathology report communicates the specimen’s origin, how it was obtained, its gross and microscopic findings, and the diagnostic interpretation. Relevant clinical information is incorporated into that interpretation. Additional studies or specialist consultations may produce supplementary reports or addenda, so the completed assessment may develop beyond the initial examination. (cancer.gov)
For cancer, pathological examination establishes important features such as tumor type, grade, involvement of sampled lymph nodes, and the status of surgical margins. Grade describes characteristics of the tumor, whereas stage concerns the extent of disease. Reports may also include biomarker results that help characterize the tumor and inform treatment planning. The information available depends on the specimen and the investigations performed. (cancer.gov)
Historical development
The development of modern pathology involved linking clinical illness to anatomical findings. Giovanni Battista Morgagni helped establish clinical–pathological correlation through the study of disease in organs. Rudolf Virchow emphasized cellular abnormalities and microscopic examination, while William Henry Welch helped establish laboratory investigation, including bacteriology, as a central activity of pathology. These approaches expanded the discipline from descriptions of diseased organs toward explanations at cellular and laboratory levels. (pubmed.ncbi.nlm.nih.gov)
Digital pathology and computational analysis
Digital pathology involves acquiring, managing, sharing, and interpreting pathological information electronically. Whole-slide scanners convert glass slides into high-resolution images that can be examined on a screen. Digital preparations support diagnostic work, consultation, teaching, research, and image analysis. Their clinical use requires validation appropriate to the intended application, including assessment of agreement with conventional microscopy. (rcpath.org)
Research using artificial intelligence explores assistance with detecting abnormalities, grading disease, and predicting treatment response from pathological images. These applications remain distinct from the simple digitization of slides. Diagnostic algorithms require validation in the specimen types and clinical settings for which they are intended, as performance demonstrated in one context does not establish suitability for every pathological task. (rcpath.org)