Risk of osteoporotic fractures in women with breast cancer: a population-based cohort study.

A population-based study was undertaken to assess the risk of osteoporotic fractures in an inception cohort of breast cancer patients and an age-matched cohort of women from the community. Prior to the index date, 9.4% of cases and 12.3% of controls (p = 0.30) had one or more osteoporotic fractures. After the index date, these proportions were 16.2 and 20.0% (p = 0.28), but follow-up was shorter for cases due to reduced survival. When duration of follow-up was accounted for in a person-years analysis, the relative risk of any fracture was 1.0 and for any osteoporotic fracture was 0.9 (95% C.I. 0.7-1.2). After adjusting for other factors in a proportional hazards model, the relative risk of any osteoporotic fracture in breast cancer cases compared to controls was 0.9. Despite contentions that breast cancer patients have more often been exposed to estrogenic factors, we found little to suggest that such women are substantially protected from osteoporotic fractures.