The use of immunohistochemistry in the differential diagnosis of primary cutaneous adnexal neoplasms and metastatic adenocarcinomas to the skin

Pathology laboratories routinely encounter cutaneous neoplasms in which the differential diagnosis includes primary tumors as well as metastatic carcinomas. This distinction is important since metastatic lesions portend a poor prognosis and, in rare cases, they can be the first sign of internal malignancy. In most cases analysis of histologic features and correlation with clinical information allow one to establish the correct diagnosis. However, occasionally, and especially in the case of adenocarcinomas, the morphologic features may be very similar in both primary cutaneous tumors (especially those of sweat gland origin) and metastatic lesions. This article reviews the use of immunohistochemistry as an adjunctive tool in the analysis of primary and metastatic carcinomas involving the skin. It also provides an algorithm including selected markers that can be used in this context.