279 Background: Peritoneal recurrence of gastric cancer after curative surgical resection is common and portends a poor prognosis. Preliminary studies suggest extensive intraoperative peritoneal lavage (EIPL) may reduce the risk of peritoneal recurrence and improve survival. We sought to perform a randomized phase III study to definitively establish the role of performing EIPL after gastrectomy. Methods: This is a prospective, open-label, phase 3 multicentre randomised controlled trial involving 22 hospitals from Korea. China, Japan, Malaysia and Singapore. Patients aged between 21 to 80 years with cT3/4 stomach cancer undergoing curative resection were randomized to either surgery and EIPL (lavage with 10 litres of saline) or surgery alone. Comparison of DFS and OS were made via log-rank test. The cumulative incidence of peritoneal recurrence was compared using competing risks approach. All analyses were performed based on intention-to-treat. Results: Between March 2015 to August 2018, 800 patients were randomly assigned to surgery alone ( n= 402) or EIPL ( n= 398). Based on a median follow-up duration of 29 months, the 3-year cumulative incidence of all-cause mortality was 23.1% and 23.3% for EIPL and surgery alone respectively (hazard ratio [HR] = 1.09, 95% CI: 0.78 to 1.52, p = 0.615). Similarly, the 3-year cumulative incidence of recurrence were 28.0% and 25.9% respectively (HR = 1.01, 95% CI: 0.74 to 1.37, p = 0.947), and 7.9% and 6.6% respectively for peritoneal recurrence (Subdistribution HR = 1.33, 95% CI: 0.73 to 2.42, p = 0.347). Overall, the risk of adverse events was higher in EIPL as compared to surgery alone (relative risk = 1.58, 95% CI 1.07 to 2.33, p = 0.019). The most common adverse events were anastomotic leak, bleeding and intra-abdominal abscess. At the planned third interim analysis on 28 August 2019, the predictive probability of achieving even a 5% difference in 3-year OS in favour of EIPL at final analysis was < 0.4%. The trial was thus recommended to terminate on the basis of futility. Conclusions: EIPL does not show any survival benefit compared with surgery alone and is not recommended for patients undergoing curative gastrectomy for cancer. Clinical trial information: NCT02140034.