Breast cancer prevention: The risks and benefits of drug therapy

Although screening recommendations have been long established, more than 40 000 women died of breast cancer in the US in the year 2001. Risk factors for developing breast cancer have been identified, leading to the possibility of breast cancer prevention. Adjuvant tamoxifen for 5 years decreases the incidence of contralateral breast cancer by 50%. This finding and the favorable safety profile of tamoxifen led to the NSABP P-1 trial, which demonstrated a 50% reduction of breast cancer in a high-risk population. The benefit was seen only in estrogen receptor (ER)-positive breast cancers, but was seen in all age groups. Furthermore, tamoxifen was found to reduce the overall rate of osteoporotic fractures. Endometrial cancer in the tamoxifen arm of the NSABP P-1 trial was increased 3- to 4-fold in women >50 years, similar to the increased risk seen with adjuvant tamoxifen therapy. Other agents that are currently under study for breast cancer chemoprevention include raloxifene and retinoids. The STAR trial is under way and compares raloxifene to tamoxifen for breast cancer chemoprevention in high-risk women. Tamoxifen is currently the only agent approved by the US Food and Drug Administration (FDA) for chemoprevention in breast cancer but has not produced a survival advantage to date.