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.
Surgical Pathology is the most significant and time-consuming branch of pathology with a primary focus on examining tissues with the naked eye or under a microscope for definitive diagnosis of disease. Surgically removed specimens are received from sources such as small biopsies of skin, core biopsies for the diagnosis of cancer, and the operating room where tumors are removed. Surgical pathology involves macroscopic (gross) and microscopic (histologic) tissue analysis where the molecular properties of tissue samples are assessed by immunohistochemistry or other laboratory tests.
Histological sections of tissue are processed for microscopic viewing using either chemical fixation or frozen section. Frozen section processing involves freezing the tissue and generating thin frozen slices of the specimen which are mounted onto glass slides. Prior to viewing the tissue under a microscope, slides processed by chemical fixation or frozen sections are either stained with chemicals or antibodies to reveal cellular components.