The hair follicle, because of the complex interplay between epithelial hair matrix and mesenchymal dermal papilla, does not readily allow routine oncologic classification. In this respect, the problems of derivation, interpretation and classification of primary neoplasms of the hair follicle are much like those of the odontogenic neoplasms. Both have in common the potential modifying factor of morphodifferentiation by stromal induction. In addition, the varied ability of the outer hair sheath to form other adnexal type cells or structures provides yet another factor in histogenesis.
From these considerations a new classification of primary neoplasms of the hair follicle is proposed. It is based on evidence derived from experimental biology,1 from a reevaluation of a number of primary clear-cell neoplasms of skin, and from a hitherto undescribed neoplasm which appears to occupy a key role in support of such a classification.
The classification specifically excludes a neoplasm or tumor-like
HEADINGTON JT, FRENCH AJ. Primary Neoplasms of the Hair FollicleHistogenesis and Classification. Arch Dermatol. 1962;86(4):430–441. doi:10.1001/archderm.1962.01590100044012