Bone mass density and risk of breast cancer and survival in older women.

Abstract

Older women with high bone mineral density (BMD) have an increased risk of breast cancer but it is not well known whether this association is associated with the stage of the tumor. The objective of the study is to determine if older women with high BMD are likely to develop a more aggressive form of breast cancer, as defined by mortality. We prospectively studied 1504 women who were 75 years of age or older at the entry in the study (range, 75-90 years), between 1992 and 1994. BMD was measured by dual-photon X-ray absorptiometry at three skeletal sites (trochanter, Ward's triangle, femoral neck). The women were followed for a mean of 7 years for the occurrence of breast cancer. Cox proportional-hazards models were used to obtain estimates of the relative risk of breast cancer and relative risk of death according to the BMD. Forty-five incident breast cancer cases were identified. In multivariate analyses of the risk of breast cancer for women in the highest tertile of BMD was greater than for women in the lowest tertile. Indeed, the women with a trochanter BMD in the highest tertile were at 2.3-fold increased risk compared with women in the lowest tertile. The women with highest tertile BMD measured at the Ward's triangle and at the femoral neck were respectively at 2.2-and 3.3-fold increased risk compared with women at the lowest risk. The 7-year survival rates were markedly less favorable for women in the second and third tertile of the three skeletal sites compared with the lowest tertile. The risk of death was greater for women in the highest tertile of BMD than for women in the lowest tertile at every skeletal site. Elderly women with high BMD have an increased risk of breast cancer, especially advanced cancer, compared with women with low BMD.