Expression of the Hair Stem Cell-Specific Keratin 15 in Pilar Tumors of the Skin

The study investigated the expression of keratin 15 (K15), a marker specific to hair follicle stem cells, in 66 cutaneous tumors with pilar differentiation. The results showed substantial reactivity in 2/2 basal cell nevi, 5/8 trichoepitheliomas, and 1/3 trichofolliculomas, while trichilemmal tumors exhibited much weaker reactivity. Pilomatricomas, basal cell carcinomas, and epidermoid cysts were completely unreactive. These findings suggested that basal cell carcinomas do not differentiate towards hair bulge cells. The study concluded that K15 immunostaining could be a useful tool for differentiating between basal cell carcinoma and trichoepithelioma.