Tamoxifen

Five trials have now reported on the use of tamoxifen and raloxifen for prevention of breast cancer [37-41]. Four trials compared 20 mg tamoxifen daily for at least 5 years with placebo [42]. One trial compared two doses faloxifen (60 mg or 120 mg) with placebo [41]. Cuzick et al. [42] report an overview of the main outcomes of hese prevention trials and adjuvant trials in which tamoxifen treatment was given for at least 3 years with doses of 20–40 mg. The combined data from tamoxifen prevention trials supported a reduction in breast cancer incidence by 38% (95% CI 28% to 46%; P <0.001). The adjuvant studies and the raloxifen trial showed greater reductions (46% [95% CI 29% to 63%] and 64% [95% CI 44% to 78%], respectively). There was no effect for breast cancers negative for oestrogen receptors (ER), but ER-positive cancers were decreased by 48% (95% CI 36% to 58%). Rates of endometrial cancer were increased in tamoxifen prevention trials (RR = 2.4, 95% CI 1.5–2.6). No increase has been seen with raloxifen. Venous thromboembolic events were increased in all tamoxifen studies and with raloxifen.

The evidence now clearly shows that tamoxifen can reduce the risk of ER-positive breast cancer. However, high rates of sideeffects do not permit a recommendation of the prophylactic use of tamoxifen in healthy women based on current evidence.