Introduction:
Breast cancer presents one of the highest rates of prevalence. With the development of genetics and biotechnology, we have learned that the occurrence and development of many cancers are closely related to abnormal gene expression. At present, some pieces of literature have reported that there may be a correlation between the expression of PCDH and the occurrence of breast cancer.Therefore, we selected some loci from PCDH gene to explore the correlation between the methylation of PCDH gene and breast cancer.

Material and methods:
This research is a systematic review and critical appraisal, make a meta-analysis of prospective and retrospective cohort study. Research was conducted through computer Science, Wanfang and Chinese knowledge network databases PubMed, Embase and Network. In a literature search, seven cohort studies were identified. This I2 statistic is used to quantify heterogeneity. A fixed effect model was used to synthesize the results. Regression tests of linear funnel plot asymmetry were used to estimate potential publication bias.

Results:
The methylation rate of PCDH gene in breast cancer with lymph node metastasis was 75%, and that in breast cancer without lymph node metastasis was 70%. The methylation rate of PCDH gene was 75% in breast cancer group with high expression of the Ki-67 gene and 71% in breast cancer group with low expression of Ki-67 gene.

Conclusions:
According to previous studies, the positive rate of methylation of PCDH gene in breast cancer tissues is higher than that in adjacent tissues, and there is no obvious statistical difference in the correlation between lymphatic metastasis and Ki-67.