Cytoplasm estrogen receptor β5 as an improved prognostic factor in thymoma and thymic carcinoma progression

A number of previous studies have reported that sex steroid hormones, including estrogens, are involved in the regulation of the thymic function. The aim of the present study was to investigate the expression of estrogen receptor β5 (ERβ5) in thymic tumors and the correlation between ERβ5 expression and thymoma biological characteristics. The expression levels of ERβ5 in thymic epithelial tumors was evaluated in 103 patents using immunohistochemical staining and reverse transcription-quantitative polymerase chain reaction. In addition, an indirect immunofluorescence assay was performed to evaluate the ERβ5 expression levels in the TC1889 and T1682 cell lines. The survival outcome was estimated using Kaplan-Meier plots. The results indicated that ERβ5 expression was mainly located in the thymic tumor cell cytoplasm (87.37%; 90/103 cases) and overexpression was observed in thymic tumors compared with normal thymic tissues (P=0.001). Using the Kruskal-Wallis test, a statistically significant association was observed between cytoplasmic ERβ5 (cERβ5) expression and thymic tumor subtypes (P=0.024) and stages (P=0.003 and R=-0.376). The Kaplan-Meier plots revealed that cERβ5 expression was significantly associated with improved overall and progression-free survival (P=0.008 and P=0.004, respectively). The present study suggested that overexpression of cERβ5 may indicate an improved prognosis and may be involved in the underlying mechanism through which estrogen inhibits thymoma and thymic carcinoma development.