Raloxifene, a
selective estrogen receptor modulator approved for the prevention and treatment of
postmenopausal osteoporosis, has shown a significant reduction in
breast cancer incidence after 3 years in this placebo-controlled, randomized clinical trial in postmenopausal women with
osteoporosis. This article includes results from an additional annual mammogram at 4 years and represents 3,004 additional patient-years of follow-up in this trial. Breast
cancers were ascertained through annual screening mammograms and adjudicated by an independent oncology review board. A total of 7,705 women were enrolled in the 4-year trial; 2,576 received placebo, 2,557
raloxifene 60 mg/day, and 2,572
raloxifene 120 mg/day. Women were a mean of 66.5-years old at trial entry, 19 years postmenopause, and osteoporotic (
low bone mineral density and/or prevalent vertebral fractures). As of 1 November 1999, 61 invasive breast
cancers had been reported and were confirmed by the adjudication board, resulting in a 72% risk reduction with
raloxifene (relative risk (RR) 0.28, 95% confidence interval (CI) 0.17, 0.46). These data indicate that 93 osteoporotic women would need to be treated with
raloxifene for 4 years to prevent one case of invasive
breast cancer.
Raloxifene reduced the risk of
estrogen receptor-positive invasive
breast cancer by 84% (RR 0.16, 95% CI 0.09, 0.30).
Raloxifene was generally safe and well-tolerated, however, thromboembolic disease occurred more frequently with
raloxifene compared with placebo (p=0.003). We conclude that
raloxifene continues to reduce the risk of
breast cancer in women with
osteoporosis after 4 years of treatment, through prevention of new
cancers or suppression of subclinical
tumors, or both. Additional randomized clinical trials continue to evaluate this effect in postmenopausal women with
osteoporosis, at risk for
cardiovascular disease, and at high risk for
breast cancer.