The pathologist has a crucial role in the diagnosis, evaluating the biopsy specimen and determining not only if it is malignant but, on the basis of his or her experience and the tissue's appearance under the microscope, the most likely source.
The pathologist is often consulted before the biopsy is done because some special immunohistochemistry studies require frozen tissue or tissue may have to be specially prepared for examination by an electron microscope. These methods were not generally available even five years ago. They offer a significant advantage in obtaining an accurate diagnosis of the primary site of origin. The limited material obtained with a needle biopsy may not be adequate for specialized pathologic studies. In such cases, an excisional biopsy may be recommended.
Immunohistochemistry Along with the usual tissue stains used to examine the tumor tissue under the microscope, special stains using monoclonal antibodies are directed against specific tumor antigens . These can often determine the likely primary site, thereby allowing therapy to be more specific and improving the chance of remission or even cure.
Special Stains Used for Specific Tissues
• The presence of keratin, a protein found in epithelium (surface tissue), indicates the tumor is a carcinoma rather
