• Have a good understanding of the study, are willing to follow the requirements of the study, and voluntarily sign the informed consent form.

• Aged ≥ 18 years old and ≤ 75 years old.

• Locally advanced unresectable or metastatic gastric or gastroesophageal adenocarcinoma confirmed by pathological histology or cytology.

• No previous systemic therapy. Note: Patients who have previously received neoadjuvant or adjuvant therapy may be enrolled if they have ended treatment without recurrence or disease progression for at least 6 months.

• Agree to provide a previously stored tumor tissue sample or a biopsy to collect tumor tissue.

• ECOG PS score is in the range of 0\

• Expected survival time ≥ 3 months.

• Subjects having adequate organ and bone marrow functions with laboratory test values within 7 days prior to enrollment meeting the following requirements (no blood components, cell growth factors, albumin, and other corrective therapy drugs are allowed to be given within the first 14 days of obtaining laboratory tests), as follows:

‣ Blood routine: absolute neutrophil count (ANC) ≥ 1.5×10\^9/L; platelet count (PLT) ≥ 75×10\^9/L; hemoglobin level (HGB) ≥ 7.5 g/dL.

⁃ Liver function: serum total bilirubin (TBIL) ≤ 1.5 × upper limit of normal (ULN); alanine aminotransferase (ALT) and aspartate aminotransferase (AST) ≤ 2.5 × ULN in subjects without liver metastases, and ALT and AST ≤ 5.0 × ULN in subjects with liver metastases; serum albumin ≥ 25 g/L.

⁃ Renal function: serum creatinine (Cr) ≤ 1.5 x ULN, or creatinine clearance\>50 mL/min.

• Female subjects of childbearing age or male subjects whose sexual partners are at childbearing age are required to take effective contraception measures throughout the treatment period and for 6 months after the treatment