Immunohistochemical distinction of cutaneous spindle cell carcinoma.

Cutaneous spindle cell squamous carcinoma is an uncommon variant of squamous cell carcinoma in which keratinocytes infiltrate the dermis as single cells with elongated nuclei rather than as cohesive nests or islands, and signs of keratinization of conventional squamous cell carcinoma are insubstantial or nonexistent. Spindle cell carcinoma must be distinguished from spindle cell/desmoplastic melanoma, cutaneous leiomyosarcoma, atypical fibroxanthoma (AFX), and scar. In instances when there is no definitive evidence of squamous differentiation, immunohistochemical studies may confer diagnostic discrimination.