Vitamin A, its physiological metabolites and synthetic derivatives (retinoids) have been shown to have protective effects against the development of certain types of cancer. In addition, pharmacological amounts of retinoids have been used with some success in the treatment of a few human tumors. The chemoprevention effect of retinoids is most likely exerted at the tumor promotion phase of carcinogenesis. Retinoids block tumor promotion by either inhibiting proliferation, inducing apoptosis, inducing differentiation, or a combination of these actions. Clinically, isotretinoin (13-cis-retinoic acid) significantly decreases the incidence of second primary tumors in patients with head and neck cancer and also reduces appearance of non-melanoma skin cancer in patients with xeroderma pigmentosum. Retinoic acid has proven to be an effective treatment for promyelocytic leukemia. However, retinoid resistance limits its use as a single agent. Clinical trials are in progress to determine the efficiency of retinoids in treating other types of cancer such as neuroblastoma and breast carcinoma. The development of receptor-selective retinoids and selective inhibitors of retinoid metabolism may lead to further use of retinoids in both chemoprevention and treatment of cancer.
Niles, R. M. (2000). Vitamin A and cancer. Nutrition, 16(7-8), 573-576.