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

Some of the nuclear retinoic acid receptors (RARs) α, β, and γ and retinoid X receptors (RXRs) α, β, and γ 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-α 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 α, β, and γ, and RXR-α 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- β 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-β. These results implicate decreases in RAR-β expression in breast cancer development and suggest that they are independent of estrogen receptor status.