This new research underscores the need to consider both genetic and nongenetic factors for personalized risk assessment in breast cancer. The key findings are: 

* Genetic risk predictors, like polygenic risk scores (PRS), do not give the full picture for breast cancer risk stratification on their own.
* We explore the epigenome-genetic interaction at methylation quantitative trait loci (mQTLs).
* Methylation levels at mQTLs vary across cell types and with epidemiological characteristics, potentially revealing non-heritable risk dynamics.
* Our WID®-qtBC index, combining methylation values at 104 mQTL sites, may enhance breast cancer risk stratification beyond PRS.