Cytokeratin expression in trichilemmal carcinoma suggests differentiation towards follicular infundibulum.

An immunohistochemical study of cytokeratins (CK) in a case of trichilemmal carcinoma (TLC). CK expression showed the presence of CK 1, 10, 14 and 17, suggesting that TLC differentiates toward follicular infundibulum. In a comparison of CK expression between TLC and trichilemmoma, the absence of CK 15 and 16 in TLC may be related to transformation from trichilemmoma to TLC. Trichilemmal carcinoma (TLC) is a rare cutaneous tumor, and is considered as a malignant counterpart of trichilemmoma. The histogenesis of TLC remains unclear. The features of TLC resemble the outer root sheath. Monoclonal antibodies against cytokeratin (CK) are crucial markers for evaluating the origin of epithelial tumors and the stage of differentiation. To elucidate the origin and the stage of differentiation of TLC, an immunohistochemical study of CK was performed using nine different anti-keratin antibodies against CK1, 7, 8, 10,14,16,17, 18 and 19.