Association between bone mineral density and incidence of breast cancer.

INTRODUCTION: Previous studies have suggested an inverse relationship between bone mineral density (BMD) and breast cancer incidence. The primary objective of this study was to assess whether BMD is associated with risk of subsequent breast cancer occurrence in the female population of southern Israel. METHODS: The electronic medical charts of women who underwent BMD at the Soroka Medical Center (SMC) between February 2003 and March 2011 were screened for subsequent breast cancer diagnoses. Women were divided by tertiles of BMD at 3 skeletal sites: lumbar spine (LS, L1-4), total hip (TH) and femoral neck (FN). The incidence of breast cancer was calculated. RESULTS: Of 15268 women who underwent BMD testing, 86 were subsequently diagnosed with breast cancer. Most women in the study were older than 50 years (94.2% and 92.7%, respectively; p = 0.597). Women who subsequently developed breast cancer had a higher mean body-mass index (BMI) (30.9 ± 5.5 vs. 29.1 ± 5.7 p = 0.004) and the mean BMD Z-score was significantly higher than in those without breast cancer for all 3 skeletal sites (LS: 0.36 ± 1.58 vs. -0.12 ± 1.42, p = 0.002; TH: 0.37 ± 1.08 vs. 0.03 ± 1.02, p = 0.002; FN: 0.04 ± 0.99 vs. -0.18 ± 0.94; p = 0.026). Women in the highest Z-score tertiles at the FN and TH had a higher chance of developing breast cancer compared to the lowest tertile; odds ratio of 2.15, 2.02, respectively (P = 0.004 and 0.01 respectively). No association was found between the BMD Z-score and the stage, histology, grade or survival from breast cancer. CONCLUSIONS: This study provides additional support for an inverse association between BMD and the risk of breast cancer.