ABSTRACT
This chapter summarizes the salient features of retinoid inhibition of cancer in two organs and addresses the mechanism of inhibition in mammary gland. Chemically induced carcinogenesis of the urinary bladder in experimental animals is a multistage process involving initiation and promotion. Inhibition of bladder carcinogenesis by retinoids was first reported by Sporn and colleagues. The majority of evidence has accumulated from studies of retinoids as chemopreventive agents for carcinogenesis of the skin, urinary bladder, and breast. The studies clearly indicate that certain retinoids are effective chemopreventive agents against chemically induced rodent mammary cancers when administered shortly after carcinogenic insult. 13-cis-retinoic acid is very effective in reversing keratinization of tracheal epithelium and in inhibiting bladder carcinogenesis but is ineffective against mammary carcinogenesis. In contrast, retinyl acetate, which is an effective chemopreventive agent for rat mammary carcinogenesis but ineffective in mice, was also ineffective in this in vitro system.
