Retinoids can reverse various premalignant lesions as well as prevent some second primary tumors. The effects of retinoids are regulated by retinoic acid receptors (RAR) and retinoid X receptors, which act as ligand-activated transcription factors. Ligand-dependent transcriptional activation of RARs is a multistep process that ends with the formation of a multimeric co-activator complex on regulated promoters. Retinoic acid receptor gamma has been shown to be the most important retinoid receptor for regulation of retinoic acid turnover rate and retinoic acid induced growth inhibition. While RAR mRNA levels may be useful biomarkers for various diseases, RAR gamma expression is decreased in Barrett's tissues compared with normal tissue.
