Dietary index scores and invasive breast cancer risk among women with a family history of breast cancer

Background: Many epidemiologic studies have analyzed the relations of individual foods and nutrients and breast cancer risk with inconsistent results. Few studies have examined recommendation-based dietary indices and breast cancer risk. Objective: The aim of this study was to determine associations between recommendation-based dietary index scores and incident invasive breast cancer. Methods: The Sister Study is a prospective cohort of 50,884 US women (baseline: 2003-2009) who had a sister with breast cancer but no prior breast cancer themselves. We created scores for the Dietary Approaches to Stop Hypertension (DASH) diet, Alternative Mediterranean Diet (AMED), and Alternative Healthy Eating Index-2010 (AHEI-2010) from dietary intakes estimated by a baseline-validated Block food-frequency questionnaire (FFQ). We used Cox regression to estimate multivariable-adjusted HRs and 95% CIs for total invasive breast cancer risk and by estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor-2 (HER2) status. Results: We documented 1,700 invasive breast cancer cases through 2015 (mean follow-up, 7.6 y). Individuals in the highest quartile of DASH scores had a lower risk of invasive breast cancer compared with those in the lowest quartile (HR: 0.78; 95% CI: 0.67, 0.90; P-trend = 0.001), with stronger associations for ER( HR: 0.61; 95% CI: 0.40, 0.94; P-trend = 0.006) as well as ER-/PR- and ER-/PR-/HER2-subtypes. AHEI-2010 (HR for highest compared with lowest quartile: 0.90; 95% CI: 0.78, 1.03; P-trend = 0.15) and AMED (HR for highest compared with lowest quartile: 0.90; 95% CI: 0.77, 1.06; P-trend = 0.07) were weakly and nonsignificantly associated with breast cancer risk, but after excluding alcohol, AHEI-2010 was inversely associated with risk of ER-/PR-(HR: 0.64; 95% CI: 0.42, 0.98; Ptrend = 0.04) and ER-/PR-/HER2-subtypes. We did not observe any significant interactions by menopausal status or other participant characteristics. Conclusions: DASH scores were inversely associated with breast cancer risk; DASH and AHEI-2010 scores excluding alcohol were particularly inversely associated with risk of ER-/PR-and ER-/PR/HER2-breast cancers. This trial was registered at clinicaltrials.gov as NCT00047970.