CpG sites located in three genes (cg06418238 in RPTOR, cg00736299 in MGRN1 and cg27466532 in RAPSN), which showed significant hypomethylation in BC patients compared to healthy controls in the discovery cohort (p < 1.00 × 10−6) were selected and successfully validated in three independent cohorts (validation I, n =211; validation II, n=378; validation III, n=520). This evidence concerns the gene MGRN1 and breast cancer.