Fracture risk among breast cancer survivors: results from the Women's Health Initiative Observational Study.

BACKGROUND: Breast cancer and its treatment may compromise bone health. We tested the hypothesis in the Women's Health Initiative Observational Study that postmenopausal survivors of breast cancer have a higher risk for fractures compared with women who have no cancer history.
METHODS: A prospective cohort (5.1 years' follow-up) study design was used. Breast cancer survivors were women who reported a history of breast cancer (n = 5298). A reference group included women who had no cancer history at baseline (n = 80 848). Fracture occurrence was ascertained from annual self-reports. Hip fractures were confirmed by reviewing medical records.
RESULTS: After adjustment for age, weight, ethnicity, and geographic region of enrollment, the hazard ratios (HRs) of breast cancer survivors to women in the reference group were 0.93 (95% confidence interval [CI], 0.64-1.33) for hip; 1.36 (95% CI, 1.16-1.59) for forearm or wrist; 1.31 (95% CI, 1.19-1.43) for eligible fractures other than hip, vertebral, and forearm or wrist; and 1.31 (95% CI, 1.21-1.41) for these fractures combined. The increased risk for clinical vertebral fracture was statistically significant only among survivors who had a breast cancer diagnosis before age 55 years (HR, 1.78; 95% CI, 1.28-2.46). After adjusting for factors related to hormone levels, risk of fall, fracture history, medication use, comorbidity, and lifestyle, the increased risk for all fractures studied among survivors was reduced to 15% (HR, 1.15; 95% CI, 1.05-1.25).
CONCLUSIONS: Postmenopausal survivors of breast cancer are at increased risk for clinical fractures. Preventions and therapeutic interventions are needed to reduce fracture risk in this large and growing population.