Preoperative Tumor Index Predicts Peritoneal Recurrence after Perioperative Chemotherapy and Resection of Gastric Cancer.

BACKGROUND: Tumor index (pathological tumor size and T stage) has been demonstrated to predict peritoneal recurrence of gastric cancer in Japan. We investigated preoperative tumor index, based on endoscopic ultrasound, and its ability to predict peritoneal recurrence despite negative staging laparoscopy, perioperative chemotherapy and R0 gastrectomy in a western cohort. METHODS: All gastric cancer patients with tumor size and depth recorded on endoscopic ultrasound, negative staging laparoscopy, and who received perioperative chemotherapy between 2008 and 2023 at a single institution, were retrospectively reviewed. Tumor index was calculated by multiplying the largest diameter (mm) of the tumor by the T stage. RESULTS: 122 patients met inclusion criteria and were followed for a median of 32 months, 99% had an R0 radical gastrectomy and 80% underwent a D2 lymphadenectomy with a median of 25 (IQR 16-34) lymph nodes examined. The median tumor index was 60 (IQR 40-128). Tumor Index ≥90 was significantly associated with peritoneal recurrence-free survival (HR 2.24, 95% CI 1.15-4.34, p=0.02). The peritoneal recurrence-free survival at 12 months was significantly lower (67%, 95%CI 51%-82%) with a tumor index ≥90 compared to those <90 (83%, 95% CI 74%-92%). The five-year overall survival was 36% with a tumor index ≥90 compared to 60% for those <90, p=0.03. CONCLUSION: Preoperative tumor index is a simple, powerful predictor of risk of peritoneal recurrence that is based on readily available parameters from staging endoscopic ultrasound. Patients with tumor index ≥90 should be considered for clinical trials to reduce peritoneal relapse and death.