Background: Carcinoembryonic antigen (CEA) and carbohydrate antigen (CA) 19-9 are well-known tumor markers. Most studies on CEA and CA 19-9 in pts with GC were performed in Asia, and/or in the metastatic setting. The aim of this study was to investigate the prognostic value of blood derived laboratory parameters in a cohort of European pts with resectable non-metastatic GC. Methods: In the CRITICS trial, 788 pts with resectable GC underwent perioperative therapy (preoperative chemotherapy plus either postoperative chemotherapy or postoperative chemoradiotherapy). Blood levels of CEA, CA 19-9, alkaline phosphatase (AP), creatinine, neutrophils, hemoglobin (Hb) and lactate dehydrogenase (LDH) were determined prior to treatment. Data for these variables were available for at least 89% of the pts. Factors significant on univariable cox regression analysis were further explored in multivariable analysis. Probabilities to undergo potentially curative surgery was investigated for factors significant on multivariable analysis. The relationship between tumor markers and the presence of circulating tumor DNA (ctDNA) was explored in 50 pts with available ctDNA data. Results: CEA and CA 19-9 were identified as independent prognostic factors for survival (Table). Probabilities to undergo potentially curative surgery were 86%, 77% and 60% for pts with no elevated tumor makers versus those with elevated CEA or elevated CA 19-9 versus those with both tumor markers elevated, respectively (p<0.001). No relationship was found between elevated tumor marker(s) and the presence of ctDNA neither pretreatment nor preoperatively. Conclusions: Pretreatment blood levels of CEA and CA 19-9 were identified as prognostic factors for overall survival in a large cohort of European GC pts with potentially curable disease. These factors may guide treatment choices at an early phase and should be included in future trials to determine their role in clinical decision making.

¹All factors were tested categorically (cut-off according to local reference). The lower category was used as reference. ²Additional included factors of which the data is not shown are age, sex, performance status (PS), Lauren classification, tumor localization and body mass index (BMI); ³Additional included factors of which the data is not shown are Lauren classification, PS and BMI. *reference.