Objectives Although the expression of estrogen receptor (ER) is usually found in uterine endometrioid adenocarcinomas, it has recently been reported to be found in some uterine serous carcinomas (USCs). This report describes the clinicopathologic features of USC with an expression of ER-α, with special reference to the prognostic significance of ER-α.

Methods The immunohistochemical expression of ER-α was examined in 33 USCs. Greater than 10% staining was defined as an overexpression of ER-α. Cox univariate and multivariate analyses for USCs were performed.

Results A total of 7 USCs (21.2%) exhibited an expression of ER-α. All tumors were pure-type USCs and strongly demonstrated an overexpression of p53. The cancer-specific 5-year survival rates of patients with USC without an expression of ER-α and USC with an expression of ER-α were 54.5% and 0.0%, respectively (P = 0.04). The univariate analyses showed an expression of ER-α to be a significant prognostic indicator in patients with USC (P < 0.05). However, multivariate analyses for USCs showed that the surgical stage was an independent prognostic factor, whereas the significance of ER immunoreactivity disappeared.

Conclusions Uterine serous carcinoma with an expression of ER-α was associated with advanced-staged tumors and a significantly worse prognosis than that without an expression of ER-α. When an endometrial biopsy specimen reveals USC with an expression of ER-α and an overexpression of p53, the presence of an extrauterine lesion is suggested.