Inhibition of mammary cancer by retinyl methyl ether.

Daily feeding of the synthetic retinoid, retinyl methyl ether, beginning one week after the oral administration of 7,12-dimethylbenz(a)anthracene to female Sprague-Dawley rats, inhibited the incidence of mammary cancer and diminished the number of mammary tumors, both malignant and benign, caused by 7,12-dimethylbenz(a)anthracene. Retinyl methyl ether also markedly increased the latent period for appearance of mammary cancers. Retinyl methyl ether caused no evident toxicity and did not affect weight gain in these experiments. This synthetic retinoid was superior to the natural retinoid, retinyl acetate, for inhibition of mammary carcinogenesis.