Abstract: Objective:To analyze the expression differences of Ki67 in different clinicopathological features,level Ⅰ andⅡ lymph nodes(LNs) in breast cancer,and explore their clinical significance.Methods:The quantity and property of Ki67 expression in 42 primary invasive breast ductal cancers were detected using immunohistochemistry,which was compared with the LNs metastasis number and location,short axis of LNs detected by MRI and related clinicopathological features.Results:The positively involved rates in levels Ⅰ and Ⅱ LNs were 74.07% and 13.33%,respectively.The quanlitative analysis demonstrated that the expression difference of Ki67 in different short axis of LNs was statistically significant(P<0.01).The quanlitative analysis showed the expression level in metastasis LNs(46.19±5.40)was significantly higher than that in non-metastasis LNs(31.19±4.79),the expression level of Ki67 in LNs with short axis ≥ 0.7cm(43.33±4.60) was significantly higher than that in LNs with short axis <0.7cm(19.17±3.32) (P<0.01),and the positive expression of Ki67 in patients with age <45 and poorly differentiated tumor(WHOⅢ) were higher(P<0.01).The Ki67 expression in WHO Ⅰ to Ⅱwere significantly related to the WHOⅢ(r=0.722,P<0.01).The Ki67 expression was not significantly related to the number of the level Ⅰ and Ⅱ LNs(P>0.05),was related to the metastasis and metastatic ratio in levelⅠ LNs(r=0.453,0.458,respectively,P<0.01),and was significantly related to the short axis of level Ⅰ LNs(r=0.689,P<0.01).Conclusions:The expression level of Ki67 in breast cancer can help to evaluate the histological grade of cancer tissue,level Ⅰ LNs short axis and metastatic involvement,which has important significance and application prospect in clinic.