Histology involves studying the structure of body tissues. Because structure is closely related to function, different tissue types are distinguishable from one another by examination of their individual components. Knowledge of the normal histology of the multitude of tissue types within the body is necessary for the recognition and understanding of disease.
The tissue on which a diagnosis is made can be taken from a patient in the operating room, a doctor's office, or from an autopsy. Autopsy is an important part of pathology which seeks to establish the cause of sudden or unexpected death, to examine disease progression, and to assist police during the investigation of criminal cases. However, most anatomic pathologists deal with tissue from living patients and a large part of this is the detection and diagnosis of cancer. A tissue diagnosis is essential before a clinician can start treatment involving major surgery, radiation, or drugs.