Abstract: Objective :To explore the significance of Maspin expression in breast cancer and lesions in breast tissues adjacent to breast cancers. Methods :S-P immunohistochemical method was used to assess the expression of Maspin in 104 invasive breast cancer, 26 breast cancer in situ,43 cases of ductal epithelial simple hyperplasia and 20 cases of epithelial dysplasia in tissues adjacent to breast cancers and 10 normal tissues.The clinical pathological significance of Maspin expression was evaluated.And the relationship between expression of Maspin and that of ER,PR,c-erbB-2, CathD,YEGF in 104 cases of invasive breast cancer was statistically analyzed. Results :Positive immunoreac-tivity was mostly located in the nuclear of normal epithelium,strong positive nuclear expression was found in all the control cases (100%). Strong nuclear expression of Maspin in simple ductal epithelial hyperplasia,dysplasia, cancer in situ and invasive breast cancer was 76.7%,65%,69.2% and 49.0%respectively,which were all lower than that of control (P<0.05).There were significant difference in the expression of Maspin between cancers and lesions in the tissue adjacent to cancer. Immunohistochemi-cal analysis showed that the Maspin plasma expression were detected in 63.5% of invasive breast cancers, 69.2% expression in cancer in situ and 85.0% expression in atypical heperplasia of tissues adjacent to cancers,51.6% simple heperplasia of tissues adjacent to cancers,but nearly no expression in normal tissues.There were also significant difference in the Maspin plasm expression between cancers and tissues adjacent to cancers or nomal tissues (P<0.01).The results of analysis by Logistic regression showed that the nuclear expression of Maspin in invasive breast cancer was positively correlated with that of ER, while negetively correlated with the expression of c-erbB-2 and histological grading. No significant correlation were found between the nuclear expression of Maspin and that of PR, Cath-D, VEGF and lymph node metastasis. The plasma expression of Maspin in invasive breast cancer were not related to any pathological parameter. Conclusions :Overexpressions of Maspin protein in nuclear was mostly in simple hyperplasia adjacent to cancers or nomal tissues, meanwhile overexpression in plasma is relatively early event in mammary carcinogenesis.It maybe act an important role in the development of breast cancer.