Clear Cell Atypical Fibroxanthoma: Clinicopathological Study of 6 Cases and Review of the Literature With Special Emphasis on the Differential Diagnosis.

Atypical fibroxanthoma (AFX) is an uncommon dermal-based neoplasm arising on the sun-damaged skin of elderly people. Clear cell AFX is a rare variant with only 12 cases reported until the present date, all of them as case reports, except for 1 small series of 3 cases. The authors report 6 new cases and review the literature with special emphasis on the differential diagnosis. The clear cell variant represents 5% of AFX from their files. Histopathologically, it consists of sheets of epithelioid, pleomorphic cells, intermixed with a varying number of giant multinucleated and spindle cells, the latter arranged in a fascicular pattern. All cell types predominantly exhibit a clear, microvacuolated cytoplasm with well-demarcated cell borders. The clinical and immunohistochemical features of this variant are similar to those of the classic type. Clear cell AFX must be differentiated from other cutaneous clear cell neoplasms, some of them with an aggressive clinical behavior, including clear cell melanoma, primary cutaneous and metastatic clear cell carcinomas, clear cell sarcoma, pleomorphic liposarcoma, tumor of perivascular epithelioid cells, and distinctive dermal clear cell mesenchymal neoplasm. The clinical presentation and immunohistochemical profile play a key role in the differential diagnosis.