Does tamoxifen prevent breast cancer?

Tamoxifen prevents breast cancer in women older than 60 years and in younger women with equally high risk because of breast disease and reproductive and family history, but there is no current evidence for or against long-term survival or overall health benefits.(Grade of recommendation A: randomized controlled trials [RCTs]) a 49% reduction in 5-year incidence of invasive and noninvasive breast cancer but increased risk for endometrial cancer, pulmonary emboli, deep vein thrombosis, and cataracts. The long-term benefits and overall health effects of tamoxifen for primary prevention of breast cancer remain unclear; the ongoing International Breast Cancer Intervention Study trial is designed to address this question