Pathology is a branch of medical science that involves the study and diagnosis of disease through the examination of surgically removed organs, tissues (biopsy samples), bodily fluids, and in some cases the whole body (autopsy). Aspects of a bodily specimen that may be considered include its gross anatomical makeup, the appearance of the cells using immunological markers, and chemical signatures in the cells. Pathology also includes the related scientific study of disease processes whereby the causes, mechanisms, and extent of disease are examined. Areas of study include cellular adaptation to injury, necrosis (death of living cells or tissues), inflammation, wound healing, and neoplasia (abnormal new growth of cells). Pathologists specialize in a wide range of diseases including cancer, and the vast majority of cancer diagnoses are made by Pathologists.

The cellular pattern of tissue samples is observed under a microscope to help determine if a sample is cancerous or non-cancerous (benign). Pathologists also employ genetic studies and gene markers in the assessment of various diseases.

Clinical Pathology concerns the laboratory analysis of blood, urine, and tissue samples to examine and diagnose disease. Typically, laboratories will process samples and provide results concerning blood counts, blood clotting ability, or urine electrolytes, for example.