PROJECT SUMMARY/ABSTRACT Cancer-related cognitive impairments (CRCI) are some of the most distressing and burdensome effects of breast cancer and its treatment. When patient reported outcomes (PROs) are used, up to 75% of survivors report CRCI. Cognitive PROs are accessible, brief, and represent everyday cognitive functioning and quality of life (QOL). Yet, cognitive PROs have been overlooked as primary outcomes in CRCI research, and there are no best practices for measurement. To move the science forward, we have to determine which cognitive PRO best reflects and predicts everyday functioning and QOL. We also need to assess CRCI within the context of survivors’ real life where competing demands are high and functioning poor. This will facilitate a better understanding of the individual variations and phenotypes of CRCI that traditional retrospective assessments may not capture. Doing so will enhance our ability to detect and quantify clinical CRCI, and better measure intervention effects aimed at improving CRCI. The proposed prospective study will collect data from 124 breast cancer survivors (BCS, ages 21+) within 1 year of completing chemotherapy (baseline) and again 2 months later (follow up). Between baseline and follow up data collection, ecological momentary assessments (EMAs) will be administered daily for 56 days (5 total: current daily activity, self-ratings of anxiety, feelings of depression, fatigue, cognitive functioning), and mobile cognitive tests (MCTs) for working memory, executive functioning, processing speed, and memory (4 total) administered every other day. We aim to 1) compare cognitive PRO predictors of everyday functioning (social function, QOL) across time and 2) determine longitudinal relationships among real life contextual factors measured by EMAs, MCTs, and cognitive PROs (at follow up). Considering the importance of PROs in healthcare research and the shift towards precision health approaches to care, the gaps in knowledge and weaknesses of research using cognitive PROs in CRCI research to date are critical. The proposed study is innovative in several ways: we will directly compare and evaluate cognitive PROs based on their ability to predict everyday functioning and QOL which has not been done before; and we will use a new methodology, intensive longitudinal assessments, to define CRCI and capture day-to-day within person variability inherent to cognitive processes. Findings from Aim 1 will provide data to inform instrument choices in CRCI practice and research. Findings from Aim 2 will establish the validity and reliability of EMAs and MCTs in BCS with CRCI and facilitate accurate and precise measurement of the lived experience. Both will facilitate rigorous observational and interventional research on CRCI in the future. Our preliminary studies and previous work strongly support our ability to carry out the proposed study. This study addresses the health promotion and prevention priority of the National Institute...