Patients in the Immediate Preoperative Anastrozole, Tamoxifen, or Combined with Tamoxifen (IMPACT) trial [17, 18], conducted by colleagues at the Royal Marsden Hospital, had oestrogen receptor positive early breast cancer and were randomised to receive aromatase inhibitor therapies (either anastrozole alone, tamoxifen alone or anastrozole and tamoxifen in combination). This evidence concerns the gene CYP19A1 and breast carcinoma.