EXPRESSION OF THE RETINOIC ACID NUCLEAR RECEPTORS (RARS) AND RETINOIDX-RECEPTOR (RXR) GENES IN ESTROGEN-RECEPTOR POSITIVE AND NEGATIVE BREAST-CANCER

Retinoid inhibition of breast carcinoma growth correlates with the est rogen receptor (ER) positivity and elevated retinoic acid nuclear rece ptor (RARalpha) mRNA levels. We therefore examined retinoid nuclear re ceptor mRNA levels in patient breast carcinoma biopsy specimens to det ermine if such a correlation exists between ER positivity and RARalpha mRNA levels. We have now shown that RARalpha mRNA levels are signific antly higher in ER positive samples. RARgamma mRNA is expressed at rel atively high levels in a majority of the tumor samples independent of the ER-status while RARbeta mRNA was expressed at low levels in only o ne tumor sample. We also found high RXRalpha mRNA levels in all of the tumor samples examined while RXRgamma mRNA could not be detected. Our study demonstrates that RARalpha mRNA levels are either low or absent in ER-negative patient samples and that RARalpha levels may serve as a potential marker to determine patient responsiveness to RA therapy.