In principle, any tamoxifen-related risks of ovarian cancer might be confounded by genetic factors, if breast cancers occurring in patients with BRCA1, BRCA2 or PeutzJeghers syndrome (which predispose to ovarian as well as breast cancer) were more, or less, likely to be treated with tamoxifen than other breast cancers. Here, BRCA2 is linked to breast carcinoma.