Lack of enhancement of experimental photocarcinogenesis by topical retinoic acid.

A controversy exists regarding the ability of retinoic acid to enhance photocarcinogenesis. Divergent results have been obtained with albino hairless mice. We examined this issue with the lightly pigmented variety. We followed two designs: 1. ultraviolet light and topical retinoic acid were given concomitantly while the retinoic acid was continued for many weeks after stopping irradiation; 2. tumors were first induced by ultraviolet light and then treated topically with retinoic acid. In both studies, retinoic acid did not enhance photocarcinogenesis with regard to latent period, tumor yield or tumor progression. It appears that different treatment schedules and different varieties of mice can produce widely disparate results.