Objective To explore the significance of gene promoter methylation of CDH1 in breast invasive ductal carcinoma.Methods The gene promoter methylation of CDH1 and E-cadherin expression status in breast cancer tissues,adjacent tissues and normal breast tissues were detected by using methylation specific polymerase chain reaction (PCR) and immunohistochemistry (SP) method.The clinicopathological data (genetic background,age,tumor size,axillary lymph node metastasis,tumor cells grading,clinical staging and molecular subtype) were collected,and analysed the clinical significance of gene promoter methylation of CDH1 in breast cancer.Results Among the 250 patients with breast cancer,113 cases were found gene promoter methylation of CDH1,and the methylation rate was 45.20％.Compared with patients with unmethylated CDH1 gene promoter,the E-cadherin protein expression was reduced in patients with methylated CDH1 gene promoter,there was statistically significant difference (x2 =21.360,P＜0.01).The univariate analysis showed that statistically significant differences were found in axillary lymph node metastasis (x2=19.086,P＜0.01),histological grading of tumor (x2 =8.487,P=0.014),CerbB-2 expression (x2=9.475,P=0.002) and molecular typing (x2 =25.482,P＜0.01) between patients with methylated and unmethylated CDH1 gene promoter.The COX regression analysis showed that there was significant difference in 5-year survival rate between patients with methylated and unmethylated CDH1 gene promoter(P＜0.01).Conclusion Methylation of CDH1 gene promoter causes decreasedexpression of mRNA,and is associated with axillary lymph node metastasis in breast cancer,which suggests that methylation of CDH1 gene promoter plays a certain role in breast cancer progression.