Arzoxifene for prevention of fractures and invasive breast cancer in postmenopausal women.

BACKGROUND: Arzoxifene is a selective estrogen receptor modulator (SERM) more potent in preclinical testing than currently available agents. Its effects on clinical outcomes are not known. METHODS: In a randomized blinded trial, women age 60 to 85 years with osteoporosis, defined as a femoral neck or lumbar spine bone mineral density T-score less than or equal to -2.5 or a vertebral fracture, and women with low bone mass, defined as a bone density T-score less than or equal to -1.0 and above -2.5, were assigned to arzoxifene 20 mg or placebo daily. The primary endpoints were new vertebral fracture in those with osteoporosis, and invasive breast cancer in the overall population. RESULTS: After 3 years, the cumulative incidence of vertebral fractures in patients with osteoporosis was 2.3% lower in the arzoxifene than in the placebo group, a 41% relative risk reduction (95% CI 0.45 to 0.77; P<0.001). In the overall population, the cumulative incidence of invasive breast cancer over 4 years was reduced by 1.3%, with a 56% relative reduction in risk (HR=0.44; 95% CI 0.26 to 0.76; P<0.001); there was no significant decrease in nonvertebral fracture risk. Arzoxifene increased the cumulative incidence of venous thromboembolic events by 0.7%, with a 2.3-fold relative increase (95% CI 1.5 to 3.7). CONCLUSION: Like other SERMs, arzoxifene decreased vertebral fractures and invasive breast cancer while the risk of venous thromboembolic events increased. (c) 2010 American Society for Bone and Mineral Research.