A Clinical Trial Evaluating TQB2102 for Injection in Combination With Behmosubaisumab/Payamprolizumab With or Without Chemotherapy in Unresectable Locally Advanced, Recurrent, or Metastatic Human Epidermal Growth Factor Receptor 2 (HER2)-Positive Gastroesophageal Adenocarcinoma

Inclusion Criteria: * 18 to 75 years of age, an Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 1, and life expectancy≥3 months; * Histopathologically confirmed unresectable locally advanced, recurrent or metastatic HER2-positive gastroesophageal adenocarcinoma; * HER2 expression levels of Immunohistochemistry(IHC) 3+ or IHC 2+ and In Situ Hybridization (ISH) positivity were confirmed in tumor tissue; * Subject is able to provide previous compliant PD-L1 expression level test results or is able to provide sufficient and competent tumor tissue for PD-L1 expression level testing; * Patients who have not received prior systemic therapy for locally advanced or metastatic gastric cancer and who have experienced tumor recurrence or metastasis at least 6 months after the completion of prior adjuvant or neoadjuvant therapy may be enrolled; * Confirmation of at least one measurable lesion according to RECIST 1.1 criteria; * The main organs function well; * Male or female patient had no plans to become pregnant and voluntarily take effective contraceptive measures from agree with the study to at least 6 months after the last dose of study drug. Exclusion Criteria: * Concurrent secondary malignancy. or other malignancy with no evidence of disease for more than 5 years; * Uncontrollable toxic reactions above CTC AE grade 1 due to any prior therapy, excluding alopecia; * Major surgical treatment, incisional biopsy or significant traumatic injury or prolonged unhealed wound or fracture within 28 days prior to first dose; * Prior history of interstitial lung disease/pneumonia (non-infectious) requiring steroidal drug intervention or current concomitant (or suspected) interstitial lung disease/pneumonia; * Arterial/venous thrombotic events, such as cerebrovascular accidents, deep vein thrombosis, and pulmonary embolism, have occurred within 6 months prior to the first dose; * Individuals with a history of psychiatric drug abuse who are unable to quit or have mental disorders; * Subjects with the presence of any severe and/or uncontrolled disease； * Subjects who have received other antitumor drugs such as chemotherapy, radiotherapy, or immunotherapy within 4 weeks prior to the first dose, or who are still within the 5 half-life of the drug (whichever occurs shortest); have received a proprietary Chinese medicine with an antitumor indication as specified in the National Medical Products Administration(NMPA) -approved drug insert within 2 weeks prior to the first dose; and have experienced any hemorrhagic or bleeding event in the month prior to the initiation of study treatment ≥CTC Patients with AE grade 3; * Subjects with known Central nervous system (CNS) metastases and/or carcinomatous meningitis * Presence of severe bone damage and spinal cord compression due to tumor bone metastases; * History of live attenuated vaccination within 28 days prior to the first dose or planned live attenuated vaccination during the study; * History of severe hypersensitivity reactions to large molecule drugs or hypersensitivity to known components of TQB2102, benmelstobart or pembrolizumab for injection; * Active autoimmune disease requiring systemic therapy (e.g., use of disease-mitigating drugs, corticosteroids, or immunosuppressive agents) within 2 years prior to the first dose of medication * Diagnosis of immunodeficiency or undergoing systemic glucocorticoid therapy or any other form of immunosuppressive therapy that was continued within 2 weeks prior to initiation of study treatment. * Participants who have participated in and used other anti-tumor clinical trial drugs within 4 weeks before the first medication use * Unstable or serious concurrent medical conditions, as assessed by the Investigators, that would substantially increase the risk-benefit ratio of participating in the study.