Clear cell carcinoma of the skin. A variant of the squamous cell carcinoma that simulates sebaceous carcinoma.

Certain clear-cell carcinomas of the skin observed in elderly caucasian men with a history of excessive sun exposure and multiple skin neoplasms may be mistaken for sebaceous carcinomas or other cutaneous clear-cell tumors. These tumors are believed to be variants of squamous cell carcinoma undergoing extensive hydropic change which results in the clear-cell appearance. They are classified into three histologic types. Type I and type III tumors are either primary or recurrent squamous-cell carcinomas. The histogenesis of type II tumors is uncertain but they may represent recurrent metastatic tumors from the previously excised, adjacent epidermal squamous-cell carcinomas; however, the possibility that they are primary adnexal tumors of undetermined histogenesis remains to be determined. Various techniques of staining, as well as differences in histologic appearance, assist in the differential diagnosis of these and other cutaneous clear-cell neoplasms.