Basal cell tumor with eccrine differentiation (eccrine epithelioma).

In 1969, Freeman and Winkelmann reported two cases of basal cell tumors with features of eccrine differentiation. On the basis of subsequent personal cases and isolated literature reports, we wish to emphasize the characteristics of this tumor. It is an infiltrating basaloid growth, usually on the scalp or head, that frequently recurs, apparently because of inadequate excision. Basaloid, alveolar, and cystic epithelial masses, which constitute the tumor, may be seen individually or together. Areas that appear to be morpheaform epithelioma or similar to syringoma can be observed. Enzyme studies reveal phosphorylase and focal lysosomal enzymes such as acid phosphatase. Acid mucopolysaccharides are present in foci. Electron microscopy shows epithelial masses with eccrine duct features. Eccrine epithelioma is a rare tumor that may be mistaken for syringoma, basal cell carcinoma, adenocystic carcinoma, sweat gland carcinoma, or metastatic tumor. Its differentiation toward eccrine structure and function predicts the chronic, recurrent, locally infiltrative clinical course observed in patients to date.