Abstract： Objective To explore the significance of BCSG1 expression in breast cancer and lesions in breast tissues adjacent to breast cancers. Methods The expression of BCSG1 was comparatively studied in in-vasive breast carcinoma (196 cases) ,atypical ductal epithelial hyperplasia adjacent to cancers(15 cases) and normal control breast tissue(10 cases) by SP immunohistochemical method and the clinical pathological signifi-cances of BCSG1 expression in invasive breast cancer were analyzed. Results Among the 10 cases normal breast tissues,only 1 case showed positive expression of BCSG1 protein in some ductal and glandular epithelia (10%),while the positive expression rate was 80% in atypical hyperplasia adjacent to cancer and 61.7% in invasive breast carcinoma,which were significantly higher than that of normal control(P<0.01). No statistical difference in the expression of BSCG1 between dysplasia and invasive cancer was found. The expression of BC-SG1 at protein level was related with the pathological grade of invasive breast carcinoma. Conclusion The ex-pressions of BCSG1 in invasive breast carcinoma and ductal epithelial dysplasia adjacent to cancer were all sig-nificantly higher than that of normal breast tissue,suggestting that BCSG1 may play a putative role in the carci-nogenesis of breast cancer.