Molecular events including gene mutation, fusion and amplification will be detected by next generation sequencing platform (OncoScreen Plus panelTM) using ctDNA collected from peripheral blood samples of gastric cancer patients. For HER2 positive patients, samples will be collected at baseline, first surveillance after treatment and disease progression. For HER2 negative patients, samples will be collected at baseline as negative control.
To identify molecular biomarker panel correlating with efficacy of trastuzuamb in advanced HER2 positive gastric cancer patients. To observe the molecular evolution of HER2 positive gastric cancer during treatment by ctDNA detection.