The pathogenesis of familial multiple cylindromas, trichoepitheliomas, milia, and spiradenomas.

Early stages in the development of hereditary cylindromas associated with trichoepitheliomas, milia, and spiradenomas revealed that (a) trichoepitheliomas were derived from the bulges of hair follicles and probably represented an abnormal histogenesis from which rarely poorly differentiated trichoepitheliomas developed; (b) milia were the result of cystic alteration of the trichoepitheliomatous bulge proliferations; and (c) cylindromas and spiradenomas were different appearances of the same tumor and developed from two separate sources, follicular bulge proliferations and eccrine glands. From the bulge proliferations multiple cylindromatous buds developed that, by increasing in number, formed the classical cylindroma and, by increasing in size rather than in number, gave the spiradenomatous variant. Eccrine glands transformed into cylindromas by cylindromatous growth from the basal cell layer. Connections between the original structures and the tumors were mostly lost. Tumors from both sources revealed the same morphology, which was most indicative of eccrine differentiation including secretory and excretory elements. Apocrine differentiation was a rare and possibly secondary event. The multiplicity in derivation and differentiation suggest an adnexal progenitor cell as the most likely source.