Osteoporosis drug proves effective against breast cancer

Initial results of the Study of Tamoxifen and Raloxifene, or STAR, show the drug raloxifene, currently used to prevent and treat osteoporosis in postmenopausal women, works as well as tamoxifen in reducing breast cancer risk for postmenopausal women at increased risk of the disease.

The UW Comprehensive Cancer Center, where tamoxifen was first recognized in 1987 as a key therapy for treating and preventing breast cancer, participated in this clinical trial, one of the largest breast cancer prevention trials ever conducted.

In STAR, both drugs reduced the risk of developing invasive breast cancer by about 50 percent. In addition, within the study, women who were prospectively and randomly assigned to take raloxifene daily, and who were followed for an average of about four years, had 36 percent fewer uterine cancers and 29 percent fewer blood clots than the women who were assigned to take tamoxifen. Uterine cancers, especially endometrial cancers, are a rare but serious side effect of tamoxifen. Both tamoxifen and raloxifene are known to increase a woman’s risk of blood clots.

STAR enrolled 19,747 postmenopausal women who were at increased risk of the disease. Among the 388 Wisconsin women who participated in the study, 94 were enrolled through the UWCCC clinical trials network in collaboration with investigators in Wausau and La Crosse. Participants were randomly assigned to receive either 60 mg of raloxifene or 20 mg of tamoxifen daily for five years.

Women taking either drug had equivalent numbers of strokes, heart attacks and bone fractures. Both raloxifene and tamoxifen are known to protect bone health; it is estimated that half a million postmenopausal women are currently taking raloxifene by prescription to prevent or treat osteoporosis. Additionally, the initial results from STAR suggest that raloxifene does not increase the risk of developing a cataract, as tamoxifen does.

The STAR researchers also tracked known menopausal side effects that occur with both drugs and monitored the participants’ quality of life. The data show that side effects of both drugs were mild to moderate in severity, and quality of life was the same for both drugs.

Participants in STAR are now receiving information about which drug they were taking. Women assigned to raloxifene will continue to be provided with the drug until they have completed five years of treatment. Those women assigned to tamoxifen can choose to continue taking tamoxifen or to receive raloxifene to complete their five years of treatment.

Women who participated in STAR were postmenopausal, at least 35 years old, and had an increased risk of breast cancer as determined by their age, family history of breast cancer, personal medical history, age at first menstrual period and age at first live birth. Before participating in the study, the women were instructed about the potential risks and benefits of tamoxifen and raloxifene and then were asked to sign an informed-consent document.