This combined analysis of more than 25,000 cases and 30,000 controls found no conclusive evidence that age at menarche, parity, age at first birth or BMI modify the established associations of breast cancer risk with 10q26-rs298158 (FGFR2), 8q24-rs13281615, 11p15-rs3817198 (LSP1), 5q11-rs889312 (MAP3K1], 16q12-rs2803662 (TOX3), 2q35-rs13387042, 5p12-rs10941679, 17q23-rs6504950, 3p24-rs4973768 and CASP8-rs17468277) nor the putative associations with TGFB1-rs1982073 or ESR1-rs3020314. This evidence concerns the gene MAP3K1 and breast cancer.