Patterns of change over time and history of the inflammatory potential of diet and risk of breast cancer among postmenopausal women.

We utilized the dietary inflammatory index (DII) to investigate associations between patterns of change in, and history of the inflammatory potential of diet and risk of breast cancer in the Women's Health Initiative (WHI). We included 70,998 postmenopausal women aged 50-79 years recruited from 1993 to 1998 into the WHI Observational Study and Dietary Modification trial control group and followed through August 29, 2014. We utilized data from food frequency questionnaires administered at baseline and Year 3, to calculate average DII scores, patterns of change in DII, and used these measures in multivariable-adjusted Cox regression models to estimate hazards ratios (HR) and 95 % confidence intervals (CI) for incident invasive breast cancer and its subtypes. After 1,093,947 person-years of follow-up, 3471 cases of invasive breast cancer were identified. There was no substantial association between average DII scores or patterns of change in DII and risk of overall invasive breast cancer (HR, 1.03; 95 % CI, 0.90, 1.17; P-trend = 0.79; comparing extreme average DII quintiles). However, there was a significant nonlinear association between average DII scores and the ER-, PR-, HER2+, subtype (HR, 2.37; 95 % CI, 1.08, 5.20; P-trend = 0.18; comparing extreme quintiles). For patterns of change in DII, the age-adjusted association with ER-, PR-, HER2+ subtype comparing women in the proinflammatory stable to those in the anti-inflammatory stable categories (HR, 1.82; 95 % CI, 1.06, 3.13) persisted in the multivariable-adjusted model but was less precise (HR, 1.85; 95 % CI, 0.96, 3.55; P = 0.06). Dietary inflammatory potential may differentially influence the development of specific breast cancer phenotypes.