ObjectiveTo study the expressions of cyclooxygenase-2(COX-2) and Ki-67 in the invasive ductal carcinoma (IDC) of breast and to analyze its clinical significance. MethodsImmunohistochemical SP method was performed to detect the expressions of COX-2 and Ki-67 in 82 cases of IDC of breast and corresponding tumor-adjacent normal breast tissues, and the relationship of these expressions to clinicopathologic characteristics was analyzed. Results①The positive rates of COX-2 and Ki-67 protein expressions in the IDC of breast tissues were significantly higher than those in the corresponding tumor-adjacent normal breast tissue [COX-2:71.95%(59/82) versus 8.54%(7/82), χ2=68.56, P < 0.001;Ki-67:64.63%(53/82) versus 13.42%(11/82), χ2=45.20, P < 0.001].②The positive rates of COX-2 and Ki-67 protein expressions were positively correlated with TNM staging (COX-2:rs=0.349, P < 0.05;Ki-67:rs=0.305, P < 0.05), lymph node metastasis (COX-2:rs=0.336, P < 0.05;Ki-67:rs=0.419, P < 0.01), vascular invasion (COX-2:rs=0.235, P < 0.05;Ki-67:rs=0.461, P < 0.01), and histological grade (COX-2:rs=0.434, P < 0.01;Ki-67:rs=0.378, P < 0.05).The positive rate of Ki-67 protein expression was positively correlated with tumor diameter (rs=0.365, P < 0.01), but the positive rate of COX-2 protein expression wasn't correlated with it (rs=0.135, P > 0.05).The positive rates of COX-2 and Ki-67 protein expressions weren't correlated with menstrual status (COX-2:rs=0.172, P > 0.05;Ki-67:rs=0.163, P > 0.05).③The positive rate of COX expression was positively correlated with the positive rate of ki-67 expression (rs=0.475, P < 0.01). ConclusionsThere are high-expressions of COX-2 and Ki-67 in IDC of breast.COX-2 and Ki-67 are significantly correlated with the clinicopathologic characteristics in IDC of breast.Combined detection of COX-2 and Ki-67 might calculate the biological behaviors of IDC of breast.COX-2 might be a target of molecular targeted therapy to breast cancer.