Primary cutaneous adnexal neoplasms and their metastatic look-alikes

Cutaneous adnexal neoplasms can often be confused with other entities, including cutaneous metastases from visceral malignancies. Distinguishing primary cutaneous adnexal neoplasms from metastases is important, as the presence of cutaneous metastases can sometimes be the first sign of an internal malignancy or, more often, can indicate a poor prognosis due to disseminated disease. Primary cutaneous adnexal tumors with clear cell histology such as sebaceous tumors or clear cell hidradenoma can mimic metastatic clear cell renal cell carcinoma. Nonmucinous primary adnexal carcinomas derived from the sweat glands can mimic adenocarcinomas metastatic from the breast, lung, gastrointestinal tract, and elsewhere. Finally, mucinous sweat gland tumors also pose a challenge as they can mimic metastatic mucinous carcinomas, particularly of the breast and gastrointestinal tract. This review includes the morphologic characteristics as well as suggested immunohistochemistry to aid in the distinction of these entities.