Hair cycle and the histogenesis of pillar tumours.

In a study of 50 tumours of pilar origin, it was observed that tumours arise from each cell type depending upon the phase of the hair cycle. Thus nevoid lesions arise from the pluripotent cells of the early anagen phase; tumours from the hair matrix, outer root sheath and inner root sheath arise during the anagen phase, and the keratoacanthomas during the interphase between anagen and telogen. Basal cell epitheliomas can arise at any phase. It was observed that the tumours arising during the anagen phase from the fully differentiated follicles formed the bulk (88%) and the keratoacanthoma simulating the catagen/telogen phase was rare in consonance with the length of each phase. It is proposed that the inner root sheath tumours be named trichilemmomas and the outer root sheath tumours trichochlamydomas to distinguish them from one another.