[Benign adnexal skin tumors]

Epithelial tumors of the cutaneous adnexae are considered to originate from three different structures, i.e., hair follicles, eccrine/apocrine sweat glands, and sebaceous glands. Although this derivation provides a practical basis for classification, some tumors may exhibit a mixed differentiation and thus should be categorized according to the prevailing phenotype. The overwhelming majority of hair follicle tumors are benign but the main diagnostic differential for malignant tumors is basal cell carcinoma. Despite a broad histological spectrum, benign tumors of sweat glands are readily recognized on the grounds of a well characterized morphology. However, it may be difficult to rule out malignancy as each benign entity has a malignant counterpart. True sebaceous neoplasms are rare when hyperplasia and hamartoma are disregarded and in extraocular locations most of them are benign.