ERβ overexpression results in endocrine therapy resistance and poor prognosis in postmenopausal ERα-positive breast cancer patients

The aim of the present study was to investigate the role of estrogen receptor (ER) beta in the prognosis of ER alpha-positive breast cancer in postmenopausal women, and its effect on the efficacy of endocrine therapy. Tissue specimens from 195 patients with postmenopausal breast cancer were analyzed. ER beta expression levels were detected using immunohistochemical staining. Kaplan-Meier analysis was performed to assess patient survival, and the difference in survival was analyzed using the log-rank test. Cox regression was utilized to evaluate prognostic factors. The results revealed that the disease-free survival rate decreased dramatically as ER beta expression levels increased in all postmenopausal ER alpha-positive breast cancer patients, and ER beta expression was identified to be an indicator of poor prognosis in cases of this disease. Similarly, in postmenopausal ER alpha-positive breast cancer patients undergoing endocrine therapy, high ER beta expression levels reduced the disease-free survival rate and were correlated with poor patient prognosis. However, in such patients who were not treated with endocrine therapy, disease-free survival rate and prognosis were not significantly affected by ER beta expression. In conclusion, ER beta overexpression led to endocrine therapy resistance and poor prognosis in postmenopausal ER alpha-positive breast cancer patients, suggesting that ER beta may affect breast cancer prognosis via an increase in endocrine therapy resistance.