ctDNA for Prediction of Relapse in Gastric Cancer

Gastric cancer is one of the common malignant tumors in China, withrelatively high incident rate and mortality among the population. 95% of the gastric cancer is adenocarcinoma. 70% of the patients at the early stage show no obvious symptom, and only small number of them has nausea, vomiting, or symptoms that are similar to the of peptic ulcer disease. Surgery is the conventional treatment option for early and middle stage gastric cancer, but postoperative relapse is the major issue. Currently, the only proven effective chemotherapies for gastric cancer are the taxane and platinum-based combination therapies. Also due to its molecular heterogeneity, the prognosis of gastric caner is highly varied among the patients. Therefore,there are not many effective targeting therapies available for the treatment of gastric cancer; and currently, trastuzumab and apatinib are the only two targeting drugs that have been clinically approved by CFDA. Circulating tumor DNA (ctDNA) is tumor-derived fragmented DNA with an average size of 166 bp, mixed with cell free DNA (cfDNA) of other sources in blood circulation (2, 3). Although the mechanisms of its release have not been fully addressed, most reports considered apoptosis and/or necrosis of tumor cells as its main sources, which makes it a genomic reservoir of different tumor clones (4). Also, as its half-life is up to hours, ctDNA is reflecting the most up-to-date status of tumor genome(5). Hence, it is considered as a new biomarker for tumor, which can be qualitative, quantitative and used for disease monitoring. By monitoring the serum ctDNA mutational profile using Next Generation Sequencing (NGS), the present clinical trial aims to elucidate the correlation between the serum ctDNA status and the prognosis of patients with early and intermediate-stage gastric cancer upon surgical treatment, and explore the possibility of clinical utility of serum ctDNA as a clinical index to predict postoperative relapse. Moreover, by comparing the molecular profiles of patients with different prognosis, we may also screen out the molecular markers related to the prognosis of gastric cancer.