Clinicopathological characteristics of estrogen receptor-β-positive human breast cancers

Recent studies have identified the presence of estrogen receptor (ER)-β in addition to ER-α in human breast cancers, but the clinicopathological characteristics of ER-β-positive tumors remain to be established. In this study, we have conducted an immunohistochemical analysis of ER-α and ER-β expression in human breast cancers. In addition, we investigated the correlation of ER-α and ER-β expression with progesterone receptor (PR) status, determined by enzyme immunoassay, and with various clinicopathological factors. Of 79 tumors, 49 (62%) were positive for ER-α and 24 (30%) were positive for ER-β, and there was no significant association between ER-α and ER-β expression. ER-α-positive tumors were significantly more likely to be PR-positive than were ER-α-negative tumors (P<0.0001), but there was no significant association between ER-β expression and PR status. However, the PR values of ER-α-positive and ER-β-positive tumors (65±17 fmol/mg protein, mean±SE) were marginally significantly lower than those of ER-α-positive and ER-β-negative tumors (340±109) (P=0.08). ER-β positivity was significantly associated with small tumor size (≤2 cm) and high histological grade (P<0.05), and this association was also observed when only ER-α-positive tumors were considered. These results suggest that determination of ER-β status might be clinically useful for further defining the characteristics of ER-α-positive tumors.