Cytokeratin profile as a clue to origin and differentiation in cutaneous squamous cell carcinoma.

Aim. Several types of squamous cell carcinoma (SCC) of the skin are recognized, even if SCCs in situ such as bowenoid actinic keratosis and Bowen's disease are histopathologically almost indistinguishable and the existance of entities such as trichilemmal carcinoma is still discussed. The aim of this study was to verify if the determination of the cytokeratin (CK) profile could be useful to better characterize some cutaneous SCCs. Methods. We studied CK1, 5, 6, 7, 8, 10, 14, 15, 16, 17, 18 and 19 expression in normal epithelial structures of the skin and in bowenoid actinic keratosis, Bowen's disease, Bowen's carcinoma, trichilemmal carcinoma, keratoacanthomatous SCC, acantholytic SCC, conventional cutaneous SCC and malignant proliferating onycholemmal cyst. Results. The most significant findings were: (a) CK17 positivity in lower follicle; (b) focal positivity for CK19 in the basal layer of the outer root sheath near the bulge; (c) CK7 positivity with CK19 negativity in the sebaceous lobules; (d) CK19 positivity in the secretory portion of both apocrine and eccrine sweat glands; (e) CK10 negativity with CK17 positivity in the nail matrix and nail bed; (f) focal expression for CK19 in several cases of Bowen's disease in contrast with its constant negativity in bowenoid actinic keratosis; (g) the almost superimposable pattern of CK expression in Bowen's disease, Bowen's carcinoma and trichilemmal carcinoma; (h) the CK10 and CK17 positivity in keratoacanthomatous SCC; (i) the lack of CK10 expression in acantholytic SCC, cutaneous conventional SCC and malignant proliferating onycholemmal cyst. Conclusion. The study was in favour of a common origin of Bowen's disease, Bowen's carcinoma and trichilemmal carcinoma from pluripotential cells of the acrothrichium and of keratoacanthomatous SCC from the lower follicle. It also showed that a strong and diffuse positivity for CK17 may be useful to differentiate keratoacanthomatous SCC from trichilemmal carcinoma in doubtful cases and that the search for CK10 expression may be useful to distinguish between well differentiated and poorly differentiated SCCs of the skin. This last statement is not true for onycholemmal carcinomas because CK10 is negative in the normal nail matrix and nail bed.