Cytokeratin 15 Expression in Trichoepitheliomas and a Subset of Basal Cell Carcinomas Suggests They Originate from Hair Follicle Stem Cells

The study suggested that trichoepitheliomas and a subset of basal cell carcinomas originated from hair follicle stem cells, specifically from the bulge area of the hair follicle. This conclusion was based on morphological and immunohistochemical analyses using an anti-CD8 monoclonal antibody that cross-reacted with cytokeratin 15 (K15), a marker for the bulge. The research involved screening 13 trichoepitheliomas, 37 basal cell carcinomas, and various other skin tumors. All trichoepitheliomas expressed K15, while only 27% of basal cell carcinomas were K15-positive. Other epidermal tumors, like squamous cell carcinomas, were K15-negative, whereas some follicular tumors, such as proliferating trichilemmal cysts, were K15-positive, supporting the hypothesis of their origin from hair follicle stem cells.