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 for hair-follicle bulge stem cells, in 66 skin tumors with pilar differentiation. It found substantial K15 reactivity in basal cell nevi, trichoepitheliomas, and trichofolliculomas, while trichilemmal tumors showed weaker reactivity. Pilomatricomas, basal cell carcinomas, and epidermoid cysts were unreactive. These findings supported the differentiation patterns of the tumors and suggested that basal cell carcinomas do not differentiate towards hair bulge cells. The study concluded that K15 immunostaining could aid in differentiating between basal cell carcinoma and trichoepithelioma.