For this study, researchers wanted to see if taking raloxifene reduces the risk of invasive breast cancer in women.
The Multiple Outcomes of Raloxifene Evaluation (MORE) was a multicenter, randomized, double-blind experiment that tracked women receiving raloxifene or placebo for a median of 40 months (SD, 3 years) at 180 clinical facilities in 25 countries, mostly in the United States and Europe, from 1994 to 1998. A total of 7705 postmenopausal women under the age of 81 (mean age, 66.5) years old were diagnosed with osteoporosis, which was defined as the occurrence of vertebral fractures or a femoral neck or spine T-score of at least 2.5 SDs lower than the mean for young healthy women. Almost the majority of the participants (96%) were Caucasian. Women with a history of breast cancer or who were on estrogen were not allowed to participate. Histopathology has verified new cases of breast cancer. In 1781 women, transvaginal ultrasonography was performed to investigate the endometrial effects of raloxifene. A chart review was used to identify whether the patient had deep vein thrombosis or pulmonary embolism.
Thirteen occurrences of breast cancer were confirmed among the 5129 women who received raloxifene, compared to 27 cases among the 2576 women who received placebo (relative risk [RR], 0.24; 95% confidence interval [CI], 0.13-0.44; P<.001). 126 women would need to be treated to prevent one instance of breast cancer. Raloxifene reduced the incidence 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 illness (RR, 3.1; 95% CI, 1.5-6.2), but not endometrial cancer (RR, 3.1; 95% CI, 1.5-6.2). (RR, 0.8; 95% CI, 0.2-2.7).