Abstract: Objective:To investigate the expression of BRCA1 protein in sporadic invasive ductal carcino -ma and to analyze its relationship with other clinicopathologic parameters.Methods:The expression of BRCA 1 protein was detected by immunohistochemistry (IHC) with Streptavidin-Peroxidase (SP) method in 67 sporadic invasive ductal carcinoma tissue samples and 53adenosis tissue samples. The clinicopathologic pa-rameters including age of onset, tumor size, axillary nodal status, estrogen receptor, progesterone receptor and Her- 2 expression were obtained from pathological documents. The expression of BRCA 1 was compared between the sporadic invasive ductal carcinoma tissues and adenosis tissues. In sporadic invasive ductal car-cinoma, the correlation between BRCA1 expression and other clinicopathologic parameters mentioned above was further analyzed. Results: The positive expression rates of BRCA1 were56.7% (38/67) in breast cancer tissues and 92.5% (49/53) in adenosis tissues. In breast cancer tissues and cancer adjacent tussues, BRCA 1 was located in the cell nucleus as well as in the cytoplasm. The expression of BRCA1 was lower in breast can-cer tissues than in cancer adjacent tissues and adenosis tissues, with a significant difference ( P<0.05). The expression of BRCA1 was positively correlated with lymph node metastasis, and negatively correlated with the expression of estrogen receptor, progesterone receptor and Her- 2 expression ( P<0.05). No correlation was found between BRCA 1 expression and age of onset or tumor size ( P>0.05). Conclusion:BRCA 1 protein may be a potential marker for estimating the biological behavior and prognosis of breast cancer.