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Introduction: The utilization of self reported chemotherapy treatment data is common in epidemiologic research but there is little understanding of its accuracy and limitations. Methods: The Mayo Clinic Breast Disease Registry (MCBDR) has over 9,600 participants enrolled within one year of a first breast cancer diagnosis. Participants receive annual follow up surveys through the mail to capture data on breast cancer treatments and outcomes. We compared nurse abstracted medical record chemotherapy data to self reported chemotherapy data from women diagnosed with stage 0 to 3 breast cancer that completed five consecutive annual follow up surveys. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) statistics were assessed for the report of broad chemotherapy receipt (yes, no, DK) within each yearly survey compared to the gold standard medical record data. To assess the accuracy of the self reported use of specific chemotherapy regimens, a sub cohort known as the “congruent sub cohort” was created for each survey year that included subjects that agreed with the nurse abstractors report of their broad chemotherapy usage. Sensitivity, specificity, PPV, NPV, and concordance statistics were calculated for the congruent sub cohorts followed by an assessment of the proportion of subjects providing correct responses for all chemotherapy regimens queried compared to those that had at least one discrepancy with the nurse abstracted data and the proportion of subjects with 0, 1, 2 and 3 or more discrepancies within each survey year. Results: For the 430 survey respondents, the average age was 59.5 years (SD 11.7) with a range of 29 to 94. The mean time between diagnosis and the year 1 follow up survey was 13.5 months, with an average of 61.2 months between diagnosis and the year 5 survey. The respondents were 97% white, 100% female, and 53.5% had a bachelor’s degree or higher. The self-reported receipt of chemotherapy had substantial agreement across all 5 follow up surveys with the nurse abstracted treatment data from the medical record with kappa values ranging from 0.70 (0.63 to 0.76) to 0.64 (0.57 to 0.71). For subjects in the congruent sub cohort (N=125, 120, 122, 121, and 121 subjects across the 5 survey years, respectively), self reported use of specific chemotherapy regimens were reported with an average concordance of 90% across the 5 annual surveys, however only 23% had perfect agreement with nurse abstracted data. The average number of discrepant responses provided by subjects was 1.2, with at least 12% of subjects reporting 3 or more erroneous responses for the specific chemotherapy regimens each survey year. Discussion: This study supports previous findings that self-reported chemotherapy usage may be utilized when resources are unavailable for medical record abstraction, but may have less utility when analyzing specific chemotherapy regimens. Citation Format: Nicole L. Larson, Kathryn J. Ruddy, Feven Abraha, Denise M. Herman, Fergus J. Couch, Janet E. Olson. Accuracy of self reported chemotherapy usage in annual follow up surveys for a breast cancer registry [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 748.