Sclerosing sweat duct (syringomatous) carcinoma.

This report describes 20 sclerosing adnexal carcinomas of the skin that recapitulate the sweat duct and share certain microscopic features with benign syringoma. Clinically, the neoplasms were slow-growing, indurated nodules or plaques. Sixteen were located on the face, including five on the upper lip. Three were situated in the axilla, and one involved the buttock. Twelve of the tumors (group 1) were composed primarily of cords and nests of whorled squamous cells with clear cell change and variable keratinization. Lumens consistent with ductal differentiation were few and isolated in some of these lesions, but others had more numerous and complex ducts. The remaining eight neoplasms (group 2) contained large numbers of small, uniform ducts, and exhibited little keratinization. Each neoplasm in the series infiltrated subcutaneous tissue or deeper tissues and was accompanied by sclerotic, fibrous stroma. Sixteen of the lesions (80%) exhibited perineural growth. One tumor involved an underlying lymph node, probably by direct extension. Cytologic atypicality was mild or lacking, and mitotic figures were sparse. Seven of 15 tumors (47%) with follow-up recurred, in some instances many years after primary excision. Tumor-free margins in the initial excision specimen appeared to be a favorable prognostic factor. The most aggressive lesion in the series showed increased cytologic atypicality in recurrences.