Surgical Conversion of Candonilimab (AK104) Plus Paclitaxel, S-1 and Apatinib for Unresectable Advanced G/GEJ Cancer

Inclusion Criteria: 1. Males or females aged ≥ 18 to ≤ 75 years at the time of signing informed consent. 2. Clinically diagnosed unresectable stage IV gastric (G) or gastroesophageal junction (GEJ) adenocarcinoma by CT/MRI/Positron Emission Tomography (PET) -CT. 3. Not received prior systemic therapy for stage IV G/GEJ adenocarcinoma 4. At least one measurable tumor lesion per RECIST v1.1; 5. Major organ functions are adequate; 6. Expected survival is ≥ 3 months; 7. Eastern Cooperative Oncology Group performance status (ECOG PS) 0-1; Exclusion Criteria: 1. Human Epidermal GrowthFactor Receptor 2 (HER2)-positive G/GEJ adenocarcinoma; 2. Previously received immune checkpoint inhibitors, including but not limited to programmed death 1 (PD-1) inhibitors and cytotoxic T lymphocyte-associated antigen-4 (CTLA-4) inhibitors; 3. Central nervous system, lung, or bone metastases; 4. Known history of active or autoimmune disease; 5. Known history of other malignancies; 6. Known history of severe cardiovascular and cerebrovascular diseases; 7. Known history of gastrointestinal bleeding within the past 3 months or significant tendency to gastrointestinal bleeding; 8. Active infection or fever of unknown origin; 9. Known history of pulmonary fibrosis, interstitial pneumonia, pneumoconiosis, radiation pneumonitis, drug-related pneumonia, and severe impairment of lung function; 10. Known history of immunodeficiency, positive HIV antibody (HIVAb) test, or other acquired or congenital immunodeficiency disorder, or active hepatitis; 11. Known history of mental disorder or psychoactive substance abuse; 12. Hypersensitivity to the drugs of this regimen;