Clinical Question

Can medication reduce breast cancer in women at above-average risk?

Bottom Line

In some postmenopausal women at higher-than-average risk of breast cancer, tamoxifen and, to a lesser extent, raloxifene (Evista) will prevent the development of breast cancer. For every 1,000 women who receive the prophylaxis, there will be seven to nine fewer cases of diagnosed breast cancer. Cancer-related mortality or overall mortality has not been shown to be affected by these preventive therapies. (Level of Evidence = 1a)

Synopsis

The authors searched several databases, including the Cochrane library, for English-language randomized controlled trials comparing estrogen-blocking treatment with placebo in women at higher-than-average risk of breast cancer but without the BRCA genetic mutation. One researcher selected studies for inclusion and abstracted the data, which were then checked by a second researcher. Two researchers evaluated the quality of the studies. Most of the patients in the studies were white, postmenopausal, and without comorbidities. Risk reduction was greatest among women with atypical hyperplasia or a five-year Gail risk model score less than 5%. Neither overall mortality nor breast cancer–related mortality were reduced by medication, although the studies were likely too short to find a difference if one existed. In four studies of tamoxifen and two studies of raloxifene, both medications reduced invasive breast cancer by 30% to 68% compared with placebo. This difference translates into seven to nine fewer women developing breast cancer out of 1,000 women treated for five years. In the single head-to-head (STAR) study, tamoxifen was more effective than raloxifene. Bone fracture rates were decreased with medication use, but endometrial cancer and cataract rates were higher with tamoxifen.

Study Information

Study design: Systematic review

Setting: Outpatient (any)

Funding source: Government

Reference: NelsonHDSmithMEGriffinJCFuRUse of medications to reduce risk for primary breast cancer: a systematic review for the U.S. Preventive Services Task Force. Ann Intern Med. 2013; 158( 8): 604– 614.