Background: Basal cell carcinoma (BCC) is still viewed by many dermatologists as a tumor of the interfollicular epidermis, although references were made early in the dermatopathologic literature to the resemblance of BCC to the hair follicle.

Objective: Our aim was to characterize the common expression pattern for the epithelial cell adhesion molecule (Ep-CAM) in BCCs, various stages of follicular embryogenesis, and adult hair follicles and, thereby, in analogy point to the similarity between BCC and the hair follicle.

Methods: We studied immunohistochemically 16 superficial BCCs for Ep-CAM and compared the expression pattern with that during hair follicle, nail, and eccrine gland development in human embryos and fetuses. In addition, we examined terminal scalp and vellus hair follicles.

Results: All BCCs expressed Ep-CAM similar to the early stages of the embryonic human hair follicle, the secondary hair germ, and the outer root sheath of the vellus hair follicle. The embryonic nail organ and the adult anagen hair follicles were completely negative.

Limitations: The conclusions are based on the similarity in the immunohistochemical expression profile for a single adhesion molecule.

Conclusion: BCC expresses the cell-cell adhesion molecule Ep-CAM similar to the embryonic hair germ, the secondary hair germ of the terminal hair follicle, and the outer root sheath of the vellus hair follicle. We suggest that this may be a clue to the adnexal nature of BCC and propose that BCC is the most primitive follicular tumor.