Abstract
CONTEXT Raloxifene hydrochloride is a selective estrogen
receptor modulator that has antiestrogenic effects on breast and
endometrial tissue and estrogenic effects on bone, lipid metabolism,
and blood clotting. OBJECTIVE To determine whether women taking raloxifene have a
lower risk of invasive breast cancer. DESIGN AND SETTING The Multiple Outcomes of Raloxifene Evaluation
(MORE), a multicenter, randomized, double-blind trial, in which women
taking raloxifene or placebo were followed up for a median of 40 months
(SD, 3 years), from 1994 through 1998, at 180 clinical centers composed
of community settings and medical practices in 25 countries, mainly in
the United States and Europe. PARTICIPANTS A total of 7705 postmenopausal women, younger than 81
(mean age, 66.5) years, with osteoporosis, defined by the presence of
vertebral fractures or a femoral neck or spine T-score of at least 2.5
SDs below the mean for young healthy women. Almost all participants
(96%) were white. Women who had a history of breast cancer or who were
taking estrogen were excluded. INTERVENTION Raloxifene, 60 mg, 2 tablets daily; or raloxifene, 60
mg, 1 tablet daily and 1 placebo tablet; or 2 placebo tablets. MAIN OUTCOME MEASURES New cases of breast cancer, confirmed by
histopathology. Transvaginal ultrasonography was used to assess the
endometrial effects of raloxifene in 1781 women. Deep vein thrombosis
or pulmonary embolism were determined by chart review. RESULTS Thirteen cases of breast cancer were confirmed among the
5129 women assigned to raloxifene vs 27 among the 2576 women assigned
to placebo (relative risk [RR], 0.24; 95% confidence interval
[CI], 0.13-0.44; P<.001). To prevent 1 case of breast
cancer, 126 women would need to be treated. Raloxifene decreased the
risk of estrogen receptor–positive breast cancer by 90% (RR, 0.10;
95% CI, 0.04-0.24), but not estrogen receptor–negative invasive
breast cancer (RR, 0.88; 95% CI, 0.26-3.0). Raloxifene increased the
risk of venous thromboembolic disease (RR, 3.1; 95% CI, 1.5-6.2), but
did not increase the risk of endometrial cancer (RR, 0.8; 95% CI,
0.2-2.7). CONCLUSION Among postmenopausal women with osteoporosis, the
risk of invasive breast cancer was decreased by 76% during 3 years of
treatment with raloxifene.
