Bone Mineral Density and Subsequent Cancer Risk

Recent cohort studies demonstrated reduced breast cancer risks among women with a history of fractures or low bone mineral density (BMD). In the Study of Osteoporotic Fractures, each standard deviation increase in distal radius BMD was associated with a 50% increased risk over three years of follow-up, while in the Framingham study, women in the highest quartile of metacarpal bone mass had a 3.5-fold higher risk than women in the lowest quartile. The impact of the severity and timing of bone loss on risk has not been investigated, and the extent to which other risk factors (family history, lifestyle, and exogenous hormones) modify the relationship with BMD is unknown.

To elaborate on these research questions, we conducted a follow-up study of postmenopausal women who volunteered for the Fracture Intervention Trial (FIT), a trial of the bone-enhancing drug alendronate. The BFIT follow-up study includes 15,595 of the 22,695 FIT volunteers. Surviving members of FIT were contacted to ascertain incident cancers and to provide updated risk factor and fracture history through a self-administered questionnaire. To supplement baseline serum samples, we used a nested case-control approach to collect buccal cell specimens for biomarker measurement, including endogenous hormones and genetic polymorphisms involved in either bone growth (e.g., vitamin D receptor) or hormone metabolism (e.g., CYPI7, COMT). Operative and pathology reports were used to validate self-reported cancers. The social security numbers and contact names provided by FIT participants at baseline facilitated comprehensive follow-up and a National Death Index search for those who could not be located.

This large cohort includes extensive baseline information on major breast cancer risk factors, and thus is ideal for evaluating potential interactions with BMD and the effects of BMD on other cancer sites. Endometrial cancer has been reported to occur more frequently among women with a history of fracture, but no previous studies have investigated its relationship to BMD. We are investigating whether proximal femur BMD predicts breast cancer risk; whether breast cancer risk factors among postmenopausal women modify the relationship with BMD; whether BMD predicts cancer risk; and whether biomarkers offer etiologic clues about BMD and cancer risk. Currently, we are examining: 1) the relationship of serum adipocytokines to endometrial cancer risk, and 2) the relationships of serum estrogens and metabolites to postmenopausal breast cancer risk. The baseline and follow-up data and the collection of additional biospecimens should enable us to answer important questions about BMD and other cancers.