Abstract The REACH study (Resilience and Equity in Aging, Cancer, and Health) assesses the impact of geriatric consultation on reducing emergency department and/or unplanned hospitalization visits (EDH) for OA age 70+ diagnosed with GI cancer. We sought to develop an OA GI cancer registry (REACH Registry) within the REACH intervention integrating 1) disease and treatment factors from the PRISSMM cancer taxonomy model with 2) patient reported outcomes and 3) geriatric assessment (GA) measures predictive of function, toxicity, and survival. We reviewed GA measures using the modified Rockwood frailty scale, PROMIS-10 global mental and physical scores, Karnofsky performance status, health-related social needs, and disease/treatment factors using PRISSMM cancer taxonomy for OA consented to REACH in the GI Cancer Center at Dana-Farber Cancer Institute (DFCI) from January 2022–April 2024. OA were eligible if age 70+ at initial DFCI consult visit and diagnosed with any GI cancer. The GA stratifies OA by frailty level on a 0-1 scale: Fit/Robust (score range 0–0.19), Pre-Frail (0.2–0.34), and Frail (0.35–1.0). PRISSMM is a cancer data modeling system developed for the American Association for Cancer Research Project Genomics Evidence Neoplasia Information Exchange (GENIE) Biopharma Collaborative; it includes pathology, radiology/imaging, symptoms, and molecular markers curated by trained research staff from unstructured EHR data. From Jan. 2022–Apr. 2024, 50 OA consented to REACH registry (94 eligible). Of those, 44% (n=22) have PRISSMM data available for analysis. Most OA reported white race (90%, n=45) and female gender (52%, n=26). Pancreatic cancer was the most common diagnosis (n=21), followed by colon (9), biliary (5), and esophageal (4). Most OA completed GA (90%, n=45) with 51% screened Fit/Robust (n=23), 47% Pre-Frail (n=21), and 2% Frail (n=1). Type 2 diabetes mellitus was the most commonly reported comorbid condition (26%, n=13), followed by chronic kidney disease (n=6) and congestive heart failure (n=3). Of the 22 OA with available PRISSMM data, 59% (n=13) were diagnosed with stage IV disease and 100% received cancer-directed therapy; 72% (n=16) received standard care, 27% clinical trial (n=6). Most OA consented for tumor somatic genomic testing (77%, n=17). At the time of data curation 24 months from assessment, 20 patients had died, 30 were alive. Evaluation of the REACH intervention geriatric consultation on EDH outcome is forthcoming. REACH registry is the first GI cancer database inclusive of geriatric specific measures alongside curated disease, treatment and genomic data. We observed a higher rate of genomic testing and treatment initiation than reported in the literature. We anticipate that by September 2024, a larger cohort of REACH Registry participants will have completed PRISSMM data available for analysis. Future study will compare EDH for REACH vs. non-REACH OA as well as treatment patterns of this OA cohort evaluated at a large comprehensive cancer center and associated community sites. Citation Format: Tammy T. Hshieh, Rachel L. Weitzner, Siri Rosenberg, Leila Rostamnjad, Lauren K. Brais, Nora Horick, Tamryn Gray, Jiping Wang, Jeffrey Meyerhardt, Nadine J. McCleary. Comprehensive genomics-informed prospective older adult (OA) cancer registry: Initial findings from gastrointestinal (GI) malignancy [abstract]. In: Proceedings of the 17th AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2024 Sep 21-24; Los Angeles, CA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2024;33(9 Suppl):Abstract nr C071.