In line with the weaker mediating effect observed for insulin in the MCCS, the reported insulin–postmenopausal breast cancer association was weaker in that study (HR per doubling concentration 1.00; 95%CI, 0.65–1.53), compared with what we observed here and with reported in a recent Mendelian randomization (MR) study (OR per genetically determined one standard deviation in insulin level 2.07; 95%CI, 1.32–3.23).47 This evidence concerns the gene INS and breast cancer.