Bone mass and the risk of breast cancer among postmenopausal women

Authors: Zhang Y, Kiel D, Kreger B, Cupples L, Ellison R, Dorgan J, Schatzkin A, et al.
Source: New England Journal of Medicine. 336:611-7. February 27, 1997.
Institutions: Boston University; Harvard University; the Framingham Study.
Financial support: National Institutes of Health; Boston University School of Medicine.



The role of estrogen in the promotion of breast cancer is difficult to quantitate. Isolated measurement of serum estrogens may not reflect long-term exposure. Studies linking estrogen replacement therapy to breast cancer are subject to bias, since most of them have been case-control studies.

Bone density in women is related, in part, to estrogen exposure. Thus, if long-term estrogen exposure increases bone density and also increases the risk of breast cancer, there should be a positive correlation between bone density and the incidence of breast cancer. This study was designed to look at this issue, using data from the Framingham study.


The Framingham study is a population-based study begun in 1948 in Framingham, Massachusetts. The original cohort included 2873 women 28 to 62 years old. Subjects were evaluated clinically approximately every two years.


Of the 1394 women who had x-rays, 21 already had a history of breast cancer and were not analyzed. Among the remaining 1373 women, breast cancer developed in 91, at a median age of 74 and at a median of 22 years after the x-ray.