Continued breast cancer risk reduction in postmenopausal women treated with raloxifene: 4-year results from the MORE trial

Raloxifene, a selective estrogen receptor modulator approved for the preven tion and treatment of postmenopausal osteoporosis, has shown a significant reduction in breast cancer incidence after 3 years in this placebo-controll ed, randomized clinical trial in postmenopausal women with osteoporosis. Th is article includes results from an additional annual mammogram at 4 years and represents 3,004 additional patient-years of follow-up in this trial. B reast cancers were ascertained through annual screening mammograms and adju dicated by an independent oncology review board. A total of 7,705 women wer e 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 o ld at trial entry, 19 years postmenopause, and osteoporotic (low bone miner al density and/or prevalent vertebral fractures). As of 1 November 1999, 61 invasive breast cancers had been reported and were confirmed by the adjudi cation board, resulting in a 72% risk reduction with raloxifene (relative r isk (RR) 0.28, 95% confidence interval (CI) 0.17, 0.46). These data indicat e that 93 osteoporotic women would need to be treated with raloxifene for 4 years to prevent one case of invasive breast cancer. Raloxifene reduced th e 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, how ever, thromboembolic disease occurred more frequently with raloxifene compa red with placebo (p = 0.003). We conclude that raloxifene continues to redu ce the risk of breast cancer in women with osteoporosis after 4 years of tr eatment, through prevention of new cancers or suppression of subclinical tu mors, or both. Additional randomized clinical trials continue to evaluate t his effect in postmenopausal women with osteoporosis, at risk for cardiovas cular disease, and at high risk for breast cancer.