An Estrogen-Related Dietary Pattern and Postmenopausal Breast Cancer Risk in a Cohort of Women with a Family History of Breast Cancer

Background: The results of previous studies on diet and postmenopausal breast cancer risk have been inconclusive, but there is some evidence that dietary patterns developed to correlate with estrogen levels are associated with breast cancer. We aimed to examine the association of a previously developed estrogen-related dietary pattern (ERDP) with postmenopausal breast cancer in the Sister Study. Methods: The ERDP was calculated from food frequency questionnaire responses among Sister Study participants without a personal history of cancer and who contributed postmenopausal person-time at risk. Cox proportional hazards models were used to estimate HRs and 95% confidence intervals for the association between the ERDP and postmenopausal breast cancer. Results: With more than 261,959 person-years of follow-up and 1,968 incident cases, the ERDP was not associated with total, invasive, estrogen receptor (ER)-positive or ER-negative subtypes of breast cancer. Results were robust to various sensitivity analyses. Conclusions: The results do not support previous studies observing a positive association between a proestrogenic dietary pattern and postmenopausal breast cancer risk. Null results may be partially explained by high levels of other breast cancer risk factors within the study population, such as a family history of breast cancer. Impact: An estrogen-related dietary pattern may not be a strong predictor of breast cancer risk in all populations. Future studies of diet and breast cancer should evaluate the potential for effect modification by family history and consider differences in dietary assessment tools when comparing results across study populations. (C) 2018 AACR.