Preventive therapy for breast cancer.

Trials with tamoxifen have clearly shown that the risk of developing oestrogen receptor-positive breast cancer can be reduced by at least 50 % with prophylactic agents. The current challenge is to find new agents which achieve this or better efficacy, but with fewer side effects. Recent results indicate that the selective estrogen-receptor modulator (SERM) raloxifene has fewer endometrial cancers, gynaecologic symptoms, and thromboembolic side effects, but is also slightly less efficacious. Results for contralateral tumours in adjuvant trials suggest that aromatase inhibitors may be able to prevent up to 70-80 % of ER-positive breast cancers, and the MAP3 trial has shown to reduce all invasive breast cancer by 65 % in the preventive setting. The IBIS-II trial is currently investigating anastrozole in healthy postmenopausal women. New agents are needed for receptor negative breast cancer and premenopausal women, and several possibilities are currently under investigation.