Evista is commonly referred to as a selective estrogen receptor modulator (SERM). In reducing the risk of invasive breast cancer, SERMs may act by blocking estrogen receptors in the breast.

Three clinical trials in 15,234 postmenopausal women comparing Evista to placebo (no drug) demonstrated that Evista reduces the risk of invasive breast cancer by 44 to 71 percent. A fourth clinical trial in 19,747 postmenopausal women at high risk for developing breast cancer compared Evista to tamoxifen. In this trial, the risk of developing invasive breast cancer was similar for the two treatments.

Evista does not completely prevent breast cancer. Breast examinations and mammograms should be done before starting Evista and regularly thereafter.