Progressive decrease in nuclear retinoic acid receptor beta messenger RNA level during breast carcinogenesis.

Some of the nuclear retinoic acid receptors (RARs) alpha, beta, and gamma and retinoid X receptors (RXRs) alpha, beta, and gamma are thought to mediate the effects of retinoids on cell growth, differentiation, and apoptosis and thereby prevent breast carcinogenesis. We analyzed the expression of mRNAs for the three RARs and RXR-alpha in histological sections of specimens from 70 breast cancer patients, which included adjacent normal tissue, ductal carcinoma in situ, and invasive cancer, using in situ hybridization. RARs alpha, beta, and gamma and RXR-alpha were expressed in 98.1, 98.0, 93.0, and 100% of the adjacent normal tissues. Significant decreases in the number of cases expressing RAR-beta were observed among ductal carcinoma in situ (83.1%) and invasive carcinomas (51.6%), especially among the poorly differentiated cases (77.4 and 35.7 %, respectively). No relationship was found between the expression of estrogen receptor and RAR-beta. These results implicate decreases in RAR-beta expression in breast cancer development and suggest that they are independent of estrogen receptor status.