Single-center, Multi-cohort Exploratory Phase Ib/II Clinical Study of First-line Treatment of Unresectable Locally Advanced/Advanced Adenocarcinoma of the Stomach or Gastroesophageal Junction Based on Different Genotypes

Inclusion Criteria:

* Voluntarily sign the informed consent form for this study.
* Male or female patients aged 18-75 years.
* unresectable advanced or metastatic gastric cancer or adenocarcinoma of the gastroesophageal junction (including indolent cell carcinoma, mucinous adenocarcinoma, hepatoid adenocarcinoma) confirmed by pathological (histological or cytological) examination.
* \>6 months from the end of prior (neo)adjuvant chemotherapy/adjuvant radiotherapy to the time of disease recurrence
* at least one measurable lesion or evaluable lesion according to RECIST version 1.1; measurable lesions should not have received local treatment such as radiotherapy (lesions located within the area of previous radiotherapy may also be optional targets if progression is confirmed and they meet RECIST 1.1 criteria)
* ECOG score: 0 to 1.
* Life expectancy ≥ 3 months.
* Adequate organ function, with the following laboratory test values required at screening.
* Routine blood test criteria to be met. Hemoglobin level (HB) ≥ 90 g/L (no blood transfusion within 14 days). Absolute neutrophil count (ANC) ≥ 1.5 x 109/L. Platelet count (PLT) ≥100×109/L (no interleukin 11 or TPO within 14 days). White blood cell count (WBC) ≥4.0×109/L (no granulocyte stimulating factor within 14 days).
* Biochemical tests are required to meet the following criteria. Serum total bilirubin (TBIL) ≤ 1.5 times the upper limit of normal (ULN). ALT and AST ≤ 2.5 ULN. Cr ≤ 1.5 ULN or creatinine clearance (CCr) ≥ 60 ml/min, (Cockcroft-Gault formula).

Serum albumin ≥ 25 g/L (2.5 g/dL). For subjects with liver metastases, AST and ALT must be ≤ 5 x ULN, leukocytes ≥ 4 x 109/L, untransfused platelets ≥ 100 x 109/L, absolute neutrophil value (ANC) without granulocyte-stimulating factor treatment ≥ 1.5 x 109/L, hemoglobin ≥ 90 g/L

* Doppler ultrasound assessment: left ventricular ejection fraction (LVEF) ≥ low limit of normal (50%).
* Adequate coagulation, defined as an international normalized ratio (INR) or prothrombin time (PT) ≤ 1.5 times ULN.
* Women of childbearing potential are required to use highly effective contraception for the duration of the study, and for the period after the last dose and for at least 180 days after chemotherapy. It is recommended that contraception be initiated at least 3 months prior to study drug administration; non-sterile men are required to use highly effective contraception for the duration of the study and for at least 180 days after both the last dose and chemotherapy. It is recommended that contraception be initiated at least 3 months prior to study drug administration.
* If local treatment of metastases, such as radiotherapy or ablation, is performed, they may also be enrolled after 14 days of washout as long as an assessable lesion is still present and the local treatment is not followed by anti-tumor therapy such as targeted, chemotherapy or immunotherapy.

Exclusion Criteria:

* Hypersensitivity to any of the test drugs and their excipients, or a history of severe allergy, or a contraindication to the test drug.
* A history or active stage of autoimmune disease.
* symptomatic/asymptomatic brain metastases
* CT suggestive of definite ulcerative lesions or positive fecal occult blood (risk of bleeding and suitability for enrollment as determined by the investigator)
* History of abnormal bleeding (except epistaxis) complained of 14 days prior to enrollment
* previous allogeneic bone marrow transplantation or organ transplantation
* congenital pulmonary fibrosis, drug-induced pneumonia, mechanized pneumonia, or CT-confirmed active pneumonia
* HIV positive test, active hepatitis B or C, active tuberculosis.
* Uncontrolled cancer pain.
* previous live attenuated vaccine within 4 weeks prior to study entry or expected to be administered during or within 5 months of the end of the trial
* Prior treatment with PD-1/PD-L1 antibodies, CTLA-4 antibodies, or other therapies targeting PD-1/PD-L1 and/or VEGFR inhibitors or have not recovered from adverse events caused by dosing \>4 weeks prior (i.e., have not returned to ≤ grade 1 or baseline levels)).
* Systemic application of glucocorticoids or immunosuppressants within 2 weeks prior to trial start (note: inhaled glucocorticoids and salicorticoids are permitted).
* Known presence of symptomatic CNS metastases and/or carcinomatous meningitis. Patients with a history of CNS metastases or spinal cord compression may be enrolled in the study if they are clearly treated and clinically stable after discontinuation of anticonvulsants and steroids for 4 weeks prior to the first dose of the study.
* Have a contraindication to hormone use.
* Have multiple factors that interfere with oral drug administration (e.g., inability to swallow, chronic diarrhea, and intestinal obstruction)
* peripheral neuropathy ≥ NCI CTCAE grade 2.
* Uncontrollable or symptomatic hypercalcemia.
* infections requiring antibiotics within 14 days prior to the start of the trial
* chronic enterocolitis.
* Patients with bone metastases at risk of paraplegia.
* Patients with any severe and/ or uncontrolled disease, including: Patients with suboptimal blood pressure control (systolic blood pressure ≥ 150 mmHg or diastolic blood pressure ≥ 100 mmHg) on antihypertensive medications; patients with class II or higher myocardial ischemia or myocardial infarction, arrhythmias (including QT interval ≥ 480 ms); class III-IV cardiac insufficiency by NYHA criteria, or cardiac ultrasound suggestive of left ventricular ejection fraction ( LVEF) \<50% in patients. Active or uncontrolled severe infections. Liver disease such as cirrhosis, decompensated liver disease, chronic active hepatitis. Poorly controlled diabetes mellitus (fasting blood glucose (FBG) \>10 mmol/L). Urine routine suggestive of urine protein ≥++ and confirmed 24-hour urine protein quantification \>1.0 g.
* Long-term untreated wounds or fractures 23) Subjects who are unable to receive a trans-peripheral central venous placement (PICC)
* Subjects with abnormal coagulation (INR \> 1.5 or APTT \> 1.5 × ULN), with bleeding tendency or on thrombolytic or anticoagulant therapy. Known hereditary or acquired bleeding and thrombotic tendencies such as: hemophilia, impaired coagulation skills, thrombocytopenia, hypersplenism, etc. Active bleeding within 14 prior to study entry.
* Major surgical procedure (craniotomy, open-heart or open-heart surgery) within 4 weeks prior to the first dose of study, or anticipated need for major surgery during study treatment, or non-diagnostic surgery within 4 weeks prior to the start of the trial.
* history of gastrointestinal perforation and/or fistula within 3 months prior to enrollment in treatment; or arterial/venous thrombotic events such as cerebrovascular accidents (except stable cerebral infarction as assessed by the investigator), deep vein thrombosis, and pulmonary embolism (except if cured)
* Clinically significant thoracoabdominal fluid, including any thoracoabdominal fluid that is detectable on physical examination, previously treated or currently still requiring treatment Those with only a small amount of thoracic ascites on imaging but asymptomatic, which the investigator assesses does not require treatment may be enrolled.
* Interstitial lung disease requiring steroid hormone therapy.
* uncontrolled metabolic disorders or other non-malignant organ or systemic diseases or secondary reactions to cancer that can lead to higher medical risk and/or uncertainty in survival evaluation
* Patients with significant malnutrition.
* Patients with a history of psychotropic substance abuse and inability to abstain or with psychiatric disorders
* those with a history of immunodeficiency, including testing positive for HIV or having other acquired, congenital immunodeficiency disorders, or a history of organ transplantation
* History of other primary malignancies, except for 1) malignancies in complete remission for at least 2 years prior to enrollment and requiring no other treatment during the study period; 2) non-melanoma skin cancers or malignant freckled nevi that have been adequately treated and have no evidence of disease recurrence; and 3) carcinomas in situ that have been adequately treated and have no evidence of disease recurrence.
* Female patients who are pregnant or breastfeeding.
* those who, in the judgment of the investigator, have a serious concomitant disease that jeopardizes patient safety or interferes with the patient's ability to complete the study
* Participating in another trial within 30 days prior to the start of the trial, or planning to participate in another trial while the trial is ongoing.
* Inclusion in the row with the most stringent conditions, if there is duplication.