An investigation of the biological basis of an interaction of abdominal fat distribution and family history of breast cancer. A nested study of sisters in the Iowa Women's Health Study (United States)

Objective: The present study examined whether levels of testosterone, sex h ormone binding globulin (SHBG), or insulin levels might underlie an increas ed risk of postmenopausal breast cancer in women with both high waist-to-hi p ratio and a family history of breast cancer disease that was noted earlie r in the Iowa Women's Health Study. Methods: Participants for the current study were selected from 1922 sister groups (3978 women) in the Iowa Women's Health Study cohort. Two groups wer e included: (1) those with no family history of breast cancer and at least one sister with a high waist-to-hip ratio; or (2) those with a positive fam ily history of breast cancer and at least one sister with a high waist-to-h ip ratio. Testosterone, SHBG and insulin were measured by radioimmunoassay from 245 fasting blood samples. Results: Familial correlations among members of 66 families were estimated at 0.32, 0.28 and 0.25 for serum insulin, free testosterone and SHBG; respe ctively. Fasting serum insulin was significantly higher in breast cancer fa mily history negative women than in family history positive women, in direc t opposition to our a priori hypothesis. No significant differences were ob served in serum SHBG or free testosterone across family history categories. Conclusion: This study corroborates a genetic component to fasting serum in sulin, free testosterone and SHBG levels. It seems unlikely that insulin, S HBG, or testosterone explain the interaction between waist-to-hip ratio and family history of breast cancer among participants in the Iowa Women's Hea lth Study.