Commentary

The IBIS investigators report the results of a well done study of tamoxifen as chemoprevention for breast cancer. Similar to 3 previously reported studies,^1–3 tamoxifen was associated with a 2 fold increase in endometrial cancers and thromboembolic events, the usual anti-oestrogenic side effects, and a comparable risk reduction in invasive and non-invasive breast cancers. An unexpected increase in overall mortality was seen; the most likely explanation for this is either chance or an increase in deaths caused by thromboembolic events. The risk of the latter (and deaths) was greatest during a 3 month postoperative period in patients having major surgery. The authors suggest that stopping tamoxifen preoperatively may be useful. It is premature to recommend this in the absence of other information. It is possible that adequate antithrombotic prophylaxis may be all that is necessary. Clearly, more data are required. Adjuvant trials of tamoxifen should also look at this issue. This large study will contribute useful information in the area of chemoprevention, but longer follow up is needed. Researchers also need to better identify high risk groups, show a survival advantage, and test agents with lower toxicity profile. Newer agents such as the aromatase inhibitors hold promise in this area and need to be tested.