BRCA1 and breast cancer: Aberrant DNA methylation is also an important mechanism in breast carcinogenesis, such as methylation in the promoter region of the tumor suppressor gene p53 [33, 34] or the homologous DNA recombination repair related gene BRCA1 [35, 36], as well as the E-cadherin promoter DNA methylation-induced loss of E-cadherin expression in basal-like breast cancer [37].