Inhibition of carcinogenesis by retinoids.

Experimental investigations of the antineoplastic effects of retinoids are reviewed in this paper. In vitro studies have shown that the hyperplastic and metaplastic response to chemical carcinogens of mouse prostate cultures is suppressed by the addition of retinoids to the culture medium, that retinoids can partially inhibit the morphologic transformation of 10T 1/2 cells by physical or chemical carcinogens, and that the growth of some non-neoplastic and some neoplastic cell lines can be inhibited by retinoids. In vivo studies have shown that retinoids can suppress papilloma and carcinoma development (the promotion phase) in the two-stage skin carcinogenesis assay, inhibit mammary and bladder carcinogenesis in mice and rats, and inhibit the growth of some transplantabletumor lines. So far it has not been possible to inhibit predictably tumour formation in the intestinal tract or the respiratory tract of rodents. Almost all the synthetic retinoids have a higher therapeutic index than the natural retinoids in the prevention or treatment of cancer.