Tricholemmal carcinoma: a study of seven cases.

Seven cases of tricholemmal carcinoma (TLC), a rarely recognized cutaneous adnexal neoplasm of external hair sheath origin, are described. Most occurred on sun-exposed skin; five involved the head and neck, one the right leg, and one the right thigh. TLC had a generally short history and all were treated by local excision. The lesions had an exophytic (3 cases) or polypoid (4 cases) gross appearance. Histologically, TLC exhibited a sharply circumscribed, lobular epithelial proliferation in continuity with the epidermis. A cytologic hallmark of these tumors was the presence of large cells with PAS-reactive, diastase-sensitive, clear or pale eosinophilic cytoplasm. High mitotic rate was a constant feature. Four tumors were infiltrative, with pushing borders, whereas three were intraepithelial. One case showed acantholysis. Immunocytochemistry revealed positivity for prekeratin and negativity for CEA and EMA, supporting the trichogenic origin of these tumors. Ultrastructural examination gave clear indication of epithelial origin for the cells but did not verify hair follicular differentiation. Despite locally aggressive growth, the clinical course of TLC appeared indolent. Moreover, there are no cases with metastases reported in the literature.