Fracture risk increases after diagnosis of breast or other cancers in postmenopausal women: results from the Women's Health Initiative.

SUMMARY: Risk for falls and fractures increases after breast cancer or other cancer diagnosis in postmenopausal women. Factors other than falls may be the major causes for the increased fracture risk.
INTRODUCTION: Cancer treatment and prognosis may have detrimental effects on bone health. However, there is a lack of prospective investigations on fracture risk among incident cancer cases.
METHODS: In this study, postmenopausal women (N = 146,959) from the Women's Health Initiative prospective cohort, who had no cancer history at baseline, were followed for up to 9 years and classified into no cancer, incident breast cancer (BC) and incident other cancer (OC) groups. The main outcomes measured were incident fractures and falls before and after cancer diagnosis. Hazards ratios (HR) and 95% confidence intervals (CI) were computed from Cox proportional hazards model.
RESULTS: While hip fracture risk before a cancer diagnosis was similar between the no cancer and cancer groups, hip fracture risk was significantly higher after BC diagnosis (HR = 1.55, CI = 1.13-2.11) and the elevated risk was even more notable after OC diagnosis (HR = 2.09, CI = 1.65-2.65). Risk of falls also increased after BC (HR = 1.15, CI = 1.06-1.25) or OC diagnosis (HR = 1.27, CI = 1.18-1.36), but could not fully explain the elevated hip fracture risk. Incident clinical vertebral and total fractures were also significantly increased after OC diagnosis (p < 0.05).
CONCLUSIONS: Postmenopausal women have significantly elevated risks for falls and fractures after a cancer diagnosis. The causes for this increased risk remained to be investigated.