Beyond 30-day mortality: causes and risk factors of half-year postdischarge mortality after gastric cancer surgery

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Background Conventional 30-day or in-hospital mortality underestimates the true burden of postoperative death after gastrectomy. This study aimed to characterize post-discharge mortality and its evolving determinants following gastric cancer surgery. Methods We retrospectively analyzed patients who underwent gastrectomy for primary gastric cancer at Seoul National University Hospital between 2013 and 2019. Mortality data were updated through national death registry linkage with complete follow-up of at least 5 years. In-hospital deaths were reviewed using medical records, while out-of-hospital deaths were classified using death certificates and family interviews. Cox regression analyses were performed across sequential postoperative intervals up to 5 years. Results Among 4802 patients included in the analysis, overall mortality within 6 months was 1.2% ( n = 57), of which 89.5% occurred after discharge. Thirty-day and 90-day mortality were 0.1% and 0.5%, respectively, demonstrating substantial underestimation by conventional short-term endpoints. Early mortality was primarily associated with emergency surgery and postoperative complications. Mid-term mortality was strongly linked to psychiatric disorders and systemic comorbidities, while low body mass index emerged as a significant predictor from 6 months onward. With longer follow-up, older age, renal or hepatic disease, multiple comorbidities, and incomplete (non-R0) resection became dominant risk factors. Tumor stage showed a strong association with mortality at 3 years. Conclusions Postoperative mortality after gastrectomy is a dynamic process extending far beyond hospital discharge and shaped by distinct risk factors over time. Because most early deaths occur after discharge, improved survival requires surveillance strategies that target high-risk patients beyond the conventional 30-day window.