PROJECT SUMMARY/ABSTRACT Diet quality indexes (DQIs) have been developed to assess dietary patterns, in contrast to a single nutrient or food, by using a hypothesis-oriented methodology. This index-based approach to dietary patterns addresses the complexity of diet, multicollinearity between dietary components, and can be readily translated into dietary recommendations. Recently, we calculated key DQIs for each participant in the Multiethnic Cohort (MEC): the Healthy Eating Index 2015 (HEI-2015), the Alternative Healthy Eating Index 2010 (AHEI-2010), the alternate Mediterranean diet (aMED) score, the Dietary Approaches to Stop Hypertension (DASH) score, and the Dietary Inflammatory Index (DII). Although these indexes have been applied to evaluate the relationship of overall diet to health outcomes including our studies on colorectal cancer in the MEC, there are limited studies addressing racial/ethnic groups other than whites, less common cancers, changes in diet quality over time, and possibility of a novel dietary pattern derived for an ethnically diverse population. To address these gaps, we will utilize the MEC that consists of more than 215,000 adults (55% women) aged 45-75 years; self-reporting as African American, Native Hawaiian, Japanese American, Latinos, or white; and completed a comprehensive survey including a validated, quantitative food frequency questionnaire (QFFQ) at cohort entry in 1993-1996. The MEC has been periodically linked to tumor registries and death files. In 2003-2007, 46% of the MEC participants completed the repeated QFFQ. The five DQIs are computed for both the baseline and the 10-year follow-up QFFQs. Specific aims to capitalize on these unique data sets include investigate the associations of the five DQIs with risk of 13 common sites of cancer (bladder, breast, endometrium, kidney, liver, lung, melanoma, non-Hodgkin lymphoma, ovary, pancreas, prostate, stomach, and thyroid) and the interplay between DQIs in cancer prevention. Next, we will examine the changes in DQIs and their associations with risk of major cancers (breast, colorectum, lung, and prostate) and mortality from all-cause, cancer, and cardiovascular disease. Our third aim is to develop a novel dietary pattern by exploring DQI components and scoring schemes as well as unique dietary features in the MEC, and validate it by examining its association with cancer risk and mortality. As dietary patterns have not been sufficiently explored for a potential anti-cancer link particularly in racial/ethnic groups other than whites, the proposed work offers a unique opportunity especially for under-studied cancers and racial/ethnic groups. The project will produce a novel dietary pattern for a multiethnic population, and ultimately could influence dietary recommendations and practices for cancer prevention and healthy aging in older adults.