This effect modification of the LUMA methylation-breast cancer association by age at menarche was evident on the multiplicative (pinteraction = 0.05), but not the additive scale [the RERI for additive interaction comparing those reporting an age at menarche ≤12 years and the highest level of global methylation assessed by LUMA (doubly exposed) to those with age at menarche >12 years and the lowest LUMA methylation levels (referent) was 0.19 (95%CI = -0.38–0.76)], [S2 Table]. This evidence concerns the gene TMEM43 and breast carcinoma.