Application of immunohistochemistry in the differential diagnosis of skin tumors.

As with neoplasms in any tissue, skin tumors may be categorized as epithelial or mesenchymal, benign or malignant, and primary or metastatic. Immunoperoxidase stains are useful in elucidating the nature of the tumor cells, especially in poorly differentiated tumors. It is important to consider that tumors may exhibit staining patterns different from the typical or reported results. This may be because of intrinsic features of the neoplasm such as the aberrant expression of antigens (markers). Furthermore, the staining of the tumor may be affected by tissue preservation and fixation as well as by the selection of antibodies used for staining. For this reason, the pathologist should be vigilant in comparing the results of unknown tumors with standard controls, with results in the literature, and with his or her own experience. Unusual neoplasms may require additional tissue for analysis, study by other ancillary methods such as electron microscopy, or consultation by more experienced laboratories. These guidelines should be helpful in providing accurate diagnosis of skin tumors.