Bone Density of Hip Connected to Breast Cancer Risk After Menopause

By Crystal Phend
TUSCON, Ariz., 29 july 2008 -- Strong bones in postmenopausal women may correlate with higher breast cancer risk, researchers said.
Each unit increase in total hip bone mineral density T-score was linked to a 25% greater risk of developing breast cancer, Zhao Chen, Ph.D., M.P.H., of the University of Arizona, and colleagues, reported in the Sept. 1 issue of CANCER.
Although the traditional Gail score was a stronger predictor -- with a 35% increased breast cancer risk for postmenopausal women with a high score -- bone mineral density modestly added to the predictive value in an analysis of the prospective Women's Health Initiative study.
The Gail risk model is a well known tool that estimates the 5-year and lifetime risk of invasive breast cancer for women 35 and older. The version of the Gail score most widely used currently includes race/ethnicity, a history of atypical hyperplasia, and a history of lobular carcinoma in situ.
Women with the highest scores on both assessments showed a sharp increase in incident breast cancer (P<0.05).
Rather than suggesting a benefit of low bone mineral density, which increases fracture risk, the study supported using clinical information from osteoporosis screening to aid breast cancer risk assessment or even as an alternative to the Gail model, the researchers said.
Other studies have also supported a link between breast cancer and bone mineral density, but this was the first to add evaluation of Gail risk assessment results in the same population of women.
The analysis included 9,941 women (average age 63) who had a dual-energy X-ray absorptiometry (DEXA) scan at one of three clinical centers in the larger Women's Health Initiative study.
During more than eight years of follow-up, 327 women developed breast cancer.
Both high bone mineral density and high Gail scores were associated with breast cancer rates.
Women with a high Gail score of at least 1.67 had an age-adjusted breast cancer incidence of 47.8 per 10,000 person-years whereas for women with lower Gail scores the incidence was 33.1 per 10,000 person-years.
Likewise, age-adjusted incidence rose with total hip bone mineral density T-score. Incidence was as follows:
For women with T-scores in the normal range, 45.5 breast cancer cases per 10,000 person-years.
For women with a low bone mineral density, 29.5 cases per 10,000 person-years.
For women with T-scores in the osteoporosis range, 11.0 cases per 10,000 person-years.
Including the Gail score and hip bone mineral density T-score together in the same model across the entire population, both assessments retained significance as independent predictors with little or no change in the hazard ratios for breast cancer risk (HR 1.47 for Gail score of 1.67 or higher, P=0.001, and HR 1.26 for higher bone density, P<0.001).
Women with both very high Gail scores and bone mineral density were found to be at an exceptionally high risk for breast cancer in the current study. However, the interaction between the Gail score and bone mineral density T-score is confined to the higher-risk groups on both measures.
Adding other major risk factors for breast cancer, including body mass index, race or ethnicity, hormone use, and smoking history, only slightly attenuated the associations (HR 1.35 for high Gail score, P=0.02, and HR 1.25 for higher bone density, P<0.001).
This suggested that confounding by known breast cancer risk factors did not account for the correlations, the researchers said. "However, considering these factors may enhance the prediction."
For the women overall and those with below-average Gail scores and total hip bone density, the two tests did not interact significantly. However, breast cancer risk increased sharply for women above the median on both scores with a significant interaction (P=0.002).
The results may have limited generalizability because of the relatively small number of minority women and the potentially more health-conscious population enrolled in the study, Dr. Chen and colleagues noted.
The study was funded by Eli Lilly.
One of the researchers reported acting as a consultant for Astra-Zeneca, Novartis, and Genentech and receiving grant support from Amgen.

Primary source: CancerSource reference:Chen Z, et al "Hip bone density predicts breast cancer risk independently of Gail score -- Results from the Women's Health Initiative" Cancer 2008; 113.