Beyond hematoxylin and eosin--the role of immunohistochemistry in surgical pathology.

Immunohistochemistry, a technique that microscopically detects cellular constituents via specific antibodies, has revolutionized the field of surgical pathology by tremendously empowering the hematoxylin and eosin (H&E) slide. In the investigation of the unknown primary, it enables detecting the origin of the tumor by use of tissue- or organ-specific antibodies as well as antibodies associated with minimal histogenetic differentiation. It has almost perfected the pathologist's ability to make specific diagnoses such as those of mesothelioma, melanoma, and neuroendocrine tumors. These diagnoses should be reached by interpreting the immunohistochemical results in the context of a detailed morphological analysis and differential diagnosis based on the H&E. Other important uses include detection of microinvasive and micrometastatic disease. Through the use of prognostic markers, immunohistochemistry can provide valuable information regarding tumor behavior and therapy. Lastly, immunohistochemistry serves a small but valuable role in highlighting microorganisms, particularly viruses.