Purpose: To examine whether bone mineral density (BMD) is predictive of breast cancer risk and mortality in a population of early postmenopausal women participating in a medical prevention program in western Austria. Patients and Methods: Between May 1991 and February 1999, lumbar spine BMD was measured by dual-energy X-ray absorptiometry (N = 1163, mean age 56.9 ± 5.7 years) or quantitative computed tomography (N = 2283, mean age 56.8 ± 5.4 years) in 3446 women aged ≥50 years. Data on medication and lifestyle factors were collected by questionnaire. Participants were prospectively followed up for breast cancer incidence, and breast cancer patients were followed up for mortality. To calculate risk of breast cancer and mortality, Cox proportional hazards models were applied. Results: During median follow-up of 20.7 years, 185 invasive breast cancer cases and 22 deaths due to breast cancer occurred. Risk of breast cancer in the highest versus the lowest BMD quartile was nonsignificantly reduced, in particular when follow-up was restricted to 10 years (hazard ratio 0.53, 95% confidence interval 0.25-1.12). There was no risk reduction when follow-up began 10 years after BMD measurement. There was no association between BMD and all-cause or breast cancer-specific mortality among breast cancer patients, but a trend toward reduced mortality risk in the highest BMD quartile. Conclusions: We hypothesize that BMD is not reflective of estrogen exposure and not predictive of breast cancer risk, at least in young postmenopausal women. Confounders such as vitamin D might underlie low breast cancer risk at high BMD, thus mirroring better health status.
Keywords: DXA; QCT; VHM&PP; bone mineral density; breast cancer.