Interaction of waist/hip ratio and family history on the risk of hormone receptor-defined breast cancer in a prospective study of postmenopausal women.

The authors previously reported an interaction of waist/hip ratio and family history on the risk of breast cancer in the Iowa Women's Health Study. Here they reexamine this association based on 9 additional years of follow-up, stratifying on tumor receptors for estrogen and progesterone. Data on risk factors and family history of breast cancer were ascertained in 1986. The occurrences of breast cancer and estrogen receptor/progesterone receptor were determined through the Iowa Surveillance, Epidemiology, and End Results' registry. Rate ratios were elevated with increasing weight and body mass index and decreasing body mass index at age 18 years, but they did not vary by family history. There was no association with height, waist circumference, or waist/hip ratio. A linear trend of increasing risk with increasing waist/hip ratio was observed among family history-positive women (p = 0.06) but not among family history-negative women (p = 0.87). This apparent interaction (p = 0.09) was examined by estrogen receptor or progesterone receptor status. When stratified on family history and estrogen receptor, no clear patterns were evident. In contrast, family history-positive women in the upper quintile of the waist/hip ratio were at 2.2-fold greater risk of progesterone receptor-negative tumors compared with those in the lowest quintile (95% confidence interval: 0.9, 5.8). Thus, the previously reported interaction between family history and waist/hip ratio is still (weakly) evident and appears to reflect risk for progesterone receptor-negative tumors.