Clear cell hidradenoma associated with the folliculo-sebaceous-apocrine unit. Histologic study of five cases

Hidradenomas are benign adnexal neoplasms of uncertain derivation. Although most investigators traditionally have considered these neoplasms to exhibit eccrine differentiation, with only occasional reports supporting apocrine derivation, subdivision of hidradenomas into two groups was recently suggested: those with eccrine differentiation (or poroid hidradenomas) and those exhibiting apocrine differentiation (or clear cell hidradenomas). We have observed five cases of clear cell hidradenomas manifesting unquestionable apocrine characteristics excised from sites other than the axilla, and displaying continuity with the epidermis through follicles. Because of the common embryologic derivation of apocrine glands, sebaceous glands, and hair follicles, and their histologic integration as the folliculo-sebaceous-apocrine unit, these findings suggest a possible origin of certain apocrine hidradenomas from pluripotential germinative cells present in follicles.