Evidence that the epidermal targets of carcinogen action are found in the interfollicular epidermis or infundibulum as well as in the hair follicles

Actively cycling, transit-amplifying cells and quiescent cells including st em cells are found in the layer of the epidermis and hair follicles. To det ermine the origin of skin tumors, we completely removed the interfollicular epidermis of carcinogen-initiated mice by an abrasion technique known to l eave the hair follicles undisturbed. The interfollicular epidermis of the a braded mice quickly regenerated from cells in the hair follicles, after whi ch time tumor promotion was begun. Mice in which the interfollicular epider mis had been removed developed papillomas and carcinomas; however, the numb er of papillomas throughout 40 weeks was half that of the unabraded mice. C arcinoma responses were not significantly different in the abraded and unab raded groups. These results are consistent with the hypothesis that the tar gets of tumor initiation are stem cells found in the hair follicles and, to a lesser degree, in the interfollicular epidermis.