CLEAR-CELL ATYPICAL FIBROXANTHOMA - AN UNCOMMON HISTOPATHOLOGIC VARIANT OF ATYPICAL FIBROXANTHOMA

Atypical fibroxanthoma is a superficial variant of pleomorphic maligna nt fibrous histiocytoma. Histopathologically, it is characterized by a dermal nodule composed of bizarre cells arranged in a haphazard-to-fa scicular pattern. These cells are spindle or rounded, pleomorphic and with numerous atypical mitotic figures. Some cells appear polygonal wi th ample and foamy cytoplasm. We recently encountered two elderly pati ents with atypical fibroxanthoma on their face. Histopathologically, o ne of the lesions was composed, almost entirely, of clear cells, where as in the other one aggregations of clear cells constituted a half of the neoplasm. Atypical multinucleated cells with a Touton-like appeara nce were present. In addition to clear cells, areas of more convention al atypical spindle cells arranged in fascicles were seen, supporting the diagnosis of atypical fibroxanthoma. PAS staining failed to demons trate glycogen in neoplastic cells. Immunohistochemistry revealed that neoplastic cells expressed positivity for vimentin, muscle-specific a ctin, and alpha smooth muscle actin, whereas cytokeratin, S-100 protei n, EMA, CEA, and desmin were negative. Ultrastructural studies showed that neoplastic cells contained abundant rough endoplasmic reticulum, mitochondria, and numerous lipid vacuoles within the cytoplasm. Clear- cell atypical fibroxanthoma is a rare variant of atypical fibroxanthom a that should be differentiated from other clear-cell neoplasms of the skin.