Based on the above selection criteria, 20 case-control studies , involving 2747 cases and 2256 controls2, 3, 4, 5, 6, 10, 15, 16, 17, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, were included to analyze the association between BRCA1 promoter methylation and sporadic breast cancer risk. This evidence concerns the gene BRCA1 and breast cancer.