BRCA1 Promoter Methylation Marks a Shared Blood Methylome State in Women with and Without Breast Cancer

Aberrant DNA methylation in peripheral blood has been proposed as a marker of breast cancer (BC) susceptibility. To determine whether BRCA1 promoter methylation reflects a broader constitutional methylation state, we performed genome-wide DNA methylation profiling in peripheral blood from 24 women with triple-negative breast cancer (TNBC) and 35 healthy controls, all carrying BRCA1 promoter methylation. Analysis using the Infinium MethylationEPIC BeadChip revealed no significant differences in global methylation patterns between groups. These findings suggest that BRCA1 promoter methylation represents a shared epigenetic state established before disease onset and largely unaffected by subsequent breast cancer development.