Clinical understaging in early gastric cancer: A common and significant problem.

333 Background: A portion of clinical stage I gastric cancer (GC) patients who undergo upfront surgery are understaged preoperatively and found to be higher stage based on final pathology, which can affect the treatment algorithm and GC outcomes. We sought to identify the incidence of understaging in this cohort and variables associated with increased risk of being understaged. Methods: Patients with clinical stage I (T1/2 N0) GC undergoing oncologic resection without neoadjuvant therapy from 2013-2020 were identified in the National Cancer Database (NCDB). Clinicopathologic predictors of understaging were identified using multivariable logistic regression. The relationship between identified variables and understaging was then modeled using logistic regression with natural cubic splines to allow for a flexible, nonlinear analysis. Cox proportional hazards analysis and Kaplan-Meier curves evaluated survival outcomes. Results: 4,370 clinical stage I GC patients were identified, of which 36.0% were initially understaged on clinical staging. Tumor size (per millimeter increase OR: 1.05, 95% CI 1.04-1.05, p