Estrogen receptor-beta messenger RNA expression in human breast tumor biopsies: Relationship to steroid receptor status and regulation by progestins

When the level of estrogen receptor (ER)-beta mRNA in tumors, determined by reverse transcription-PCR, was assessed according to either ER status or P R status alone, determined by ligand binding assays, the level of ER-beta m RNA was significantly lower in PR+ tumors compared with PR- tumors (P = 0.0 36), and no association with ER status was found, Subgroup analysis showed that ER-beta mRNA expression in ER+/PR+ breast tumors was significantly les s than in ER+/PR- (P = 0.009), ER-/PR+ (P = 0.029), and ER-/PR- (P = 0.023) groups. Interestingly, the ER-beta mRNA expression was specifically decrea sed by progestin in T-47D breast cancer cells. The data suggest the possibi lity that expression of ER-beta in human breast tumors is a marker of endoc rine therapy responsiveness.