Objective To study the expression status of estrogen receptor-alpha36(ER-α36)in breast cancer tissue and its rela-tionships with the occurrence,development and clinical prognosis of breast cancer.Methods 653 cases of breast cancer tissues were selected in this study.The real-time reverse transcription polymerase chain reaction(RT-PCR)and immunohistochemistry were used to detect the expression of ER-α36,estrogen receptor-alpha66 (ER-α66),progesterone receptor(PR)and human epidermal growth factor receptor-2(Her-2).The relationships between the expression of ER-α36,ER-α66,PR and Her-2 and the pathological charac-ter were analyzed.Results The expression rate of ER-α36 in all cases was 40%.The expression rate of ER-α36 in Her-2 positive tissues(63%)was significantly higher than that in the Her-2 negative group(44%,P <0.05).The expression rate of ER-α36 in ER-α66/PR/Her-2 negative tissues(66%)was significantly higher than that in the non-three-negative group(35%,P <0.05).The differences of ER-α36 expression rate between ER-α66 positive samples and negative samples or between PR positive and negative samples showed no statistical significance(P >0.05).The expression rate of ER-α36 in stage Ⅲ+Ⅳ breast cancer tissues(54%) was significantly higher than that in stage Ⅰ+Ⅱ breast cancer tissues(28%,P <0.05).The expression rate of ER-α36 in breast cancer tissues with lymph node metastasis (55%)was significantly higher than that in breast cancer tissues without lymph node me-tastasis (23%,P <0.05).Conclusion The results indicate that ER-α36 may play a very important role in the occurrence,develop-ment and lymph node metastasis of breast cancer,and be associated with the expression of Her-2,breast cancer staging and lymph node metastasis.ER-α36 is expected to become a new tumor marker and clinical diagnosis and treatment target.