Keratin protein immunohistochemistry in surgical pathology practice.

Keratin protein immunohistochemistry is a powerful diagnostic tool whose role has already been firmly established in many surgical pathology laboratories. Recent studies of the biology of keratin proteins have defined the heterogeneity of keratin protein expression among various epithelial tissues and their tumors and provide the basis for understanding the immunoreactivity of epithelial tumors with various keratin antibodies. Successful execution of the procedure requires attention to technical details such as the fixation of tissue, use of proteolytic enzymes such as trypsin for formalin-fixed tissues, and the choice of the appropriate antibody and controls. Broadly reactive polyclonal and monoclonal antibodies to keratins have been remarkably useful in identifying poorly differentiated and undifferentiated carcinomas. Monoclonal antibodies of restricted specificity and monospecific antibodies to keratin are under development and may prove helpful in defining the organ of origin of metastatic carcinomas. Keratin protein immunohistochemistry supplements existing information used by pathologists in diagnosis, and the immunohistochemical results should be interpreted in the light of the clinical findings, gross and microscopic pathology, and the results of any other special studies.