Our previous analyses demonstrate that the reduction in breast cancer risk for carriers of the rare allele of rs10235235 (which is correlated with the CYP3A7*1C allele r2=0.25, D'=1.0) is very modest (heterozygote OR=0.98, P=0.2; homozygote OR=0.80, P=0.004; Johnson et al, 2014) consistent with an unfavourable (reduced) 2-hydroxylation:16α-hydroxylation counteracting a potentially more substantial beneficial effect of lower levels of parent oestrogens. Here, CYP3A7 is linked to breast cancer.