e15548 Background: The benefit of adjuvant treatment in gastric adenocarcinoma patients with muscularis propria involvement but not beyond is unclear. We aim to establish a model that identifies the factors that could adversely affect the prognosis in these patients, whom could potentially benefit from adjuvant treatment. Methods: We used the Surveillance, Epidemiology, and End Results Program (SEER) database to identify subjects with stage T2aN0M0 gastric adenocarcinoma according to the 6th AJCC TNM staging system who underwent tumor resection between 2004-2015. The effect of the following factors on the 5-year overall survival (OS) was evaluated using Kaplan-Meier analysis: demographics, tumor size, grade and site, number of lymph nodes (LNs) being examined and extent of surgery. Factors with a P value < 0.1% in log-rank test were entered in a Cox proportional hazard ratio (HR) model. Results: We identified 1337 patients who met the inclusion criteria. After a median follow-up of 42 months (1-60), the 5-year OS was 64% with the median being unreached. The following factors were significantly associated with shorter OS in univariate analysis: Age > 60 years with a HR = 1.86 (95% CI 1.49-2.32), Non-Hispanics excluding non-Hispanic Asian and Pacific Islanders with a HR = 1.87 (95% CI 1.54-2.28), patients with less than 15 lymph nodes examined at the time of surgery with a HR = 1.86 (95% CI 1.52-2.26), tumors at the fundus and cardia of the stomach compared to other sites with a HR = 1.73 (95% CI 1.37-2.15), those who underwent endoscopic resection with a HR = 2.27 (95% CI 1.16-4.4) and those who didn’t receive chemotherapy with a HR = 1.23 (95%CI 1.001-1.52) . On multivariate analysis; the following factors were predictors for worse OS; Age > 60 years with a HR = 1.97 (95% CI 1.46-2.65), Non-Hispanics excluding non-Hispanic Asian and Pacific Islanders with a HR = 1.45 (95%CI 1.10-2.00), those in whom less < 15 LNs were examined at the time of surgery with a HR = 1.75 (95% 1.38-2.22) and gastric adenocarcinoma at the cardia and fundus with a HR = 1.50 (95%CI 1.20-1.86). Conclusions: Patients with T2aN0M0 gastric adenocarcinoma, and one of the adverse prognostic factors in our Cox-proportional hazard ratio model need to be studied for possible benefit of adjuvant treatment.