Abstract Background: In the United States, over 60% of breast cancer survivors are 65 years and older; however, little is known about patient-reported symptoms and the effect that cancer treatments could have on survivors years after their primary treatment and diagnosis. This study evaluated perceived cognitive function in older breast cancer survivors and whether prior chemotherapy was associated with cognitive outcomes. Methods: Breast cancer patients aged 65 years and older, diagnosed 2012-2013, with local and regional stage disease, were identified through the linked Texas Cancer Registry-Medicare dataset (TCR). Survivors were mailed a survey to assess their cognitive function through the Functional Assessment of Cancer Therapy-Cognitive Function (FACT-Cog V3) instrument (section G of the survey). The survey also collected demographic and clinical data and was collected between April 2018 and October 2019. Utilizing the data from the self-administered questionnaires, TCR, and Medicare claims, the cognitive function and quality of life among elderly patients were evaluated to assess whether prior chemotherapy and/or endocrine therapy impacts long-term health. A linear regression model was used to examine the significance of receiving chemotherapy to FACT-Cog V3 primary score while controlling for respondent sociodemographic and clinical variables. Results: Of 4,448 eligible patients, 1,954 (43.9% response rate) responded to section G. Of these, 1,065 respondents completed all 4 sections, 37 questions. Eighty of those 1065 respondents self-reported disease recurrence which excluded them from the analyses in order to avoid biases, leaving a total of 985 cases for this study. Median time from diagnosis to survey completion was 68 months (IQR 62-73). Receipt of chemotherapy was associated with a slightly lower FACT-Cog score. In total, those with chemotherapy scored, on average, 105.6 (SD 21.2) while those without scored 107.1 (SD 22.3). The largest difference in mean scores is attributed to the Perceived Cognitive Impairment subsection (scored from 0-72) where those with chemotherapy scored, on average, 57.2 (SD 13.8) and those without scored 58.7 (SD 14.0). Responsible Conduct Of Research: We need to ensure that the privacy of our patients will be protected when using their information from the surveys. Conclusion: Adjuvant chemotherapy was associated with more self-reported cognitive impairment in older breast cancer survivors, even 5-6 years after diagnosis. However, the difference between patients who received chemotherapy versus those who did not was modest, suggesting limited clinical significance. Further research is needed to determine the long-term impact of cancer treatments, particularly in older cancer survivors. Citation Format: Rachel Kim, Kai-Ping Liao, Susan Peterson, Daria Zorzi, Liang Li, Mariana Chavez MacGregor, Sharon Giordano. Cognitive function in older breast cancer survivors after chemotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 7454.