Low Expectancy of Conversion Surgery with R0 Resection in Patients with CEA > 5.0 ng/mL at the Initial RECIST Evaluation for Metastatic Gastric Cancer

SIMPLE SUMMARY: This study aimed to identify early predictive factors associated with the success of conversion surgery with R0 resection in patients with metastatic gastric cancer who underwent systemic chemotherapy. Patients with carcinoembryonic antigen > 5.0 ng/mL at the initial Response Evaluation Criteria in Solid Tumors evaluation showed less expectancy of undergoing conversion surgery with R0 resection. ABSTRACT: This retrospective study examined early the predictive factors for successful conversion surgery (CS) with R0 resection in patients with metastatic gastric cancer (MGC) who underwent systemic chemotherapy. This study included 204 patients diagnosed with metastatic gastric adenocarcinoma, who received chemotherapy between 2009 and 2019. Of these patients, 31 (15%) underwent CS with R0 resection. The incidence of CS with R0 resection was not affected by the volume of metastatic lesions or the presence of peritoneal metastasis. The overall survival time of the CS with R0 resection group was significantly longer than that of the non-CS group (hazard ratio, 0.12; 95% confidence interval, 0.07–0.23; p < 0.0001), with a 5 year overall survival rate of 50.2%. Multivariate analysis of 150 patients, excluding those with disease progression until the initial Response Evaluation Criteria in Solid Tumors (RECIST) evaluation, showed that carcinoembryonic antigen > 5.0 ng/mL at the initial RECIST evaluation was an independent, significant, and unfavorable predictor of CS with R0 resection (odds ratio, 0.21; p = 0.0108), whereas systemic chemotherapy with trastuzumab for HER2-positive cancer was a favorable factor (odds ratio, 4.20; p = 0.0119). Monitoring serum carcinoembryonic antigen levels during chemotherapy may be a useful predictor of the CS implementation in patients with MGC.