Gastric cancer is among the most common malignant tumors nationwide with high morbidity and mortality. Attributing to its insidious onset and rapid progress, 70% of patients with gastric cancer were initially diagnosed at an advanced stage. In advanced gastric cancer, systemic treatment based on chemotherapy drugs, targeted drugs, and immune checkpoint inhibitors remains the main regimens. Among current standard treatment regimens, though HER2-positive and MSI-H/dMMR statuses indicate the treatment efficacy of trastuzumab and immune checkpoint inhibitors, there is still lack of robust biomarkers for predicting treatment efficacy. Tumor microenvironment as pivotal components of solid tumor, significantly influences therapeutic response and clinical outcome. The study is a multi-center, observational study to evaluate the relationship between standard treatment efficacy and the tumor microenvironment in advanced gastric cancer. In addition, the study comprehensively evaluated the landscape of the tumor microenvironment characteristics of gastric cancer, and aimed at establishing robust biomarkers for predicting prognosis and treatment efficacy to finetune treatment strategies.

Gastric cancer is among the most common malignant tumors nationwide with high morbidity and mortality. Attributing to its insidious onset and rapid progress, 70% of patients with gastric cancer were initially diagnosed at an advanced stage. In advanced gastric cancer, systemic treatment based on chemotherapy drugs, targeted drugs, and immune checkpoint inhibitors remains the main regimens. Among current standard treatment regimens, though HER2-positive and MSI-H/dMMR statuses indicate the treatment efficacy of trastuzumab and immune checkpoint inhibitors, there is still lack of robust biomarkers for predicting treatment efficacy. Tumor microenvironment as pivotal components of solid tumor, significantly influences therapeutic response and clinical outcome. The study is a multi-center, observational study to evaluate the relationship between standard treatment efficacy and the tumor microenvironment in advanced gastric cancer. In addition, the study comprehensively evaluated the landscape of the tumor microenvironment characteristics of gastric cancer, and aimed at establishing robust biomarkers for predicting prognosis and treatment efficacy to finetune treatment strategies. Eligible subjects were selected according to the inclusion criteria and exclusion criteria. After successful screening, the patients were treated following the clinical guidelines and the actual conditions. The residual tissue samples of the primary tumor or metastatic foci were collected to conduct the tumor microenvironment detection analysis.

Inclusion Criteria:

1. Histologically or cytologically confirmed advanced gastric cancer.
2. Willing to receive anti-tumor drug treatment.
3. Willing to provide residual tumor tissues after routine clinical diagnosis for tumor microenvironment detection analysis.
4. Eastern Cooperative Oncology Group (ECOG) performance status score of 0 to 1.
5. At least one measurable lesion or non-measurable but evaluable as defined by RECIST 1.1.

Exclusion Criteria:

1. Human epidermal growth factor receptor 2 (HER2) is positive, that is, tissue immunohistochemical staining (IHC) (3+) or IHC (2+), and tissue fluorescence in situ hybridization (FISH) is positive.

Patients with histologically or cytologically confirmed advanced gastric cancer.