Gastric cancer is one of the common malignant tumors in China, with relatively high incident rate and mortality among the population. More than 80% of gastric cancer are in advanced stage.~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.ctDNA is reflecting the most up-to-date status of tumor genome. Hence, it is considered as a new biomarker for tumor, which can be qualitative, quantitative and used for disease monitoring. Detecting ctDNA, in most patients, allows for the noninvasive molecular characterization detection of tumors, including genetic changes that are revealed by the selective pressure of therapies. Considering the origin of ctDNA, it can be from different subclones of primary tumor or both primary and metastatic tumors, the ctDNA may overcome the problems caused by tumor heterogeneity. Additionally, the short half-life of ctDNA, about 2 hours, makes ctDNA an ideal dynamic marker of tumor bulk.~Molecular events including gene mutation, fusion and amplification will be detected by next generation sequencing platform using ctDNA collected from peripheral blood samples of gastric cancer patients. Samples will be collected at baseline, every two months in the surveillance after treatment and disease progression.~Thus, the objective of this study is to identify a prognostic and/or predictive biomarker of tumor response according to the tumor DNA circulating assessment in gastric cancer treatment, in order (i) to avoid an unnecessary toxicity of an ineffective treatment that it would be continued uselessly, (ii) and to allow a early changing to an alternative therapy regimen.
This study aims to evaluate the use of next generation sequencing (NGS) to detect circulating tumor DNA in advanced HER2 negative gastric cancer patients. The evaluation of the therapy efficacy for gastric cancer patients is usually evaluated by computer tomography scans with RECIST criteria that are performed every two months during the treatment. In this study, we will compare the monitoring of circulating tumor DNA with the results of CT scan according the RECIST criteria and the blood level of CEA and CA 19-9 tumor markers.