BRCA1 and breast cancer: Our study found BRCA1 promoter hypermethylation in 41.67% (20/48) of malignant breast tumors (MBTs) and 46.67% (7/15) of normal adjacent tissues (NATs) (Figure 1c and Table S1), strengthening a similar methylation profile between MBTs and NATs (Figure 1c and Table S1).