Effects of retinoids on ultraviolet-induced carcinogenesis.

The evidence for effects of the retinoids on UV-induced carcinogenesis is sparse. Clinical observations indicate that topical RA can cause significant regression of premalignant actinic keratoses. Also there is some evidence that this agent can cause dissolution of some basal cell epitheliomas. However this latter effect does not appear to be of therapeutic value. Systemic retinoids are of little value in the treatment of premalignant and malignant cutaneous lesions though 13-cis-retinoic acid might be of use in the basal cell nevus syndrome. Examination of the influence of the retinoids on photocarcinogenesis essentially has been confined to RA and animal experimentation. RA in nontoxic concentrations can both stimulate and inhibit photocarcinogenesis depending upon the circumstances of the study. The mechanisms of these responses are not clear. Influences on DNA synthesis directly and/or indirectly or on immune responses may be involved in both effects. Preliminary studies with oral 13-cis-retinoic acid have not demonstrated any effects to date on UV-induced skin cancer formation.