Tamoxifen use and osteoporotic fracture risk: a population-based analysis.

PURPOSE: Although tamoxifen has been shown to increase bone mineral density in clinical trials, it is less clear whether this significantly affects fracture rates. Even fewer data are available on skeletal outcomes when tamoxifen is used outside of the context of a clinical trial. A population-based case-control study was undertaken to determine whether tamoxifen use is associated with osteoporotic fractures in routine clinical practice. PATIENTS AND METHODS: Population-based administrative data for the Province of Manitoba, Canada, were examined for tamoxifen use and nontraumatic fracture codes in women 50 years of age or older. Women with osteoporotic fractures (vertebral, wrist or hip; n = 11,096) from 1996 to 2004 were each compared with three controls without fracture, matched for age, ethnicity, and comorbidity (n = 33,209). Tamoxifen use was classified as never, past use, or current use.
RESULTS: Lower osteoporotic fracture rates were associated with current tamoxifen use (univariate odds ratio [OR] = 0.68; 95% CI, 0.55 to 0.84). After controlling for demographic and medical diagnoses known to affect fracture risk, current use was associated with a significantly reduced overall osteoporotic fracture risk (adjusted OR = 0.68; 95% CI, 0.55 to 0.88) and of hip fractures (adjusted OR = 0.47; 95% CI, 0.28 to 0.77). Neither recent nor remote past tamoxifen use was associated with reduced osteoporotic fracture risk. Breast cancer was not independently associated with osteoporotic fractures (adjusted OR = 0.95; 95% CI, 0.81 to 1.12).
CONCLUSION: In a population-based case-control study, current tamoxifen use was associated with a substantial reduction in osteoporotic fractures.