Overall, there were 14,119 ER + /PR + breast cancer cases and 32,418 controls for this subgroup analysis, but for what was, arguably, the most pertinent subgroup (i.e., current oestrogen–progesterone therapy use), the number of cases who were current users was relatively small (CYP3A7*1C carriers N = 107, non-carriers N = 1498) and power was limited to detect modest interactions. Here, CYP3A7 is linked to breast carcinoma.