Gastric cancer displays significant global variation in incidence, with the highest rates observed in Eastern Asia, Eastern Europe and South America [1]. Current treatment guidelines recommend that chemotherapy should be administered for 2–4 months prior to surgery, and resumed thereafter, for a total of about 6 months of chemotherapy [3,4]. Despite this combined treatment, the long-term survival of non-metastatic gastric cancer remains limited, with a 36% 5-year overall survival rate [2]. While the pathological response to preoperative chemotherapy has been associated with relapse-free and overall survival [5], no biological or imaging tool is able to detect and quantify minimal residual disease, i.e., residual cancer cells after chemotherapy and/or surgery that are responsible for subsequent metastatic relapse. Circulating tumor biomarkers have demonstrated their clinical validity in several non-metastatic cancer types either as baseline prognostic biomarkers, as a monitoring tool during preoperative chemotherapy and/or as a way to detect minimal residual disease [6,7,8,9,10,11,12,13,14,15,16,17,18,19,20]