BRCA1 and breast carcinoma: Because there was only one study26 in which the tissue of the control group was derived from patients with benign breast diseases, we omitted the study to evaluate the frequency of BRCA1 promoter methylation in breast cancer tissues compared with normal breast tissues, and the pooled OR was 7.23 (95%CI 4.35–12.01, P < 0.00001), which showed that the frequency of BRCA1 methylation in breast carcinoma tissues was 7.23-fold higher than that in normal breast tissues.