TRICHOBLASTOMA AND BASAL-CELL CARCINOMA ARE NEOPLASMS WITH FOLLICULARDIFFERENTIATION SHARING THE SAME PROFILE OF CYTOKERATIN INTERMEDIATE FILAMENTS

Trichoblastoma and nodular basal cell carcinoma are generally held to be distinctive epithelial neoplasms with some overlapping features. We investigated 30 trichoblastomas in which the basaloid cells expressed cytokeratins (CK) CK5/6, CK14, CK17, CK19, and, in a few cells, vimen tin. The cells of the periphery of small and large cysts showed the sa me profile. Cells lining the lumen of small cysts expressed CK14, CK17 , and involucrin, and those in larger cysts showed a positivity for CK 1, CK4, CK10, CK14, CK17, and involucrin. The remaining rested antibod ies (CK7, CK8, CK13, CK18, CK20, a-smooth-muscle actin) were negative in all cases. The cells of the stroma expressed vimentin and in 22 cas es, the CD34 antigen. Seventeen nodular basal cell carcinomas showed e xactly the same staining pattern. Furthermore, there are striking immu nohistochemical similarities between the neoplastic basaloid cells of both neoplasms and the cells of the hair germ. Therefore, trichoblasto ma and nodular basal cell carcinoma cannot be distinguished by their p attern of cytokeratin expression in par affin sections. The virtually identical cytokeratin pattern seen in trichoblastoma, basal cell carci noma, and the developing fetal hair follicle is compelling evidence fo r a common differentiation pathway.