JS107 vs Investigator's Choice as Second-line or Later Therapy for Advanced CLDN18.2-Positive Gastricor GEJ Adenocarcinoma.

Prior treatment

• Previous treatment with any drug or cellular therapy targeting CLDN18.2 (except CLDN18.2 monotarget monoclonal antibody).
• Previously treated with an ADC loaded with a tubulin inhibitor.
• Received strong CYP3A inhibitor or inducer within 2 weeks or 5 half-lives prior to randomization, whichever is longer.
• Use of chemotherapy, immunotherapy or other anti-tumor therapies or participation in other clinical trials within 3 weeks prior to randomization, or use of oral fluorouracil, small molecule targeted drugs or traditional Chinese medicine for gastric cancer within 2 weeks prior to randomization.
• Major surgery (requiring general anaesthesia and \>24 hours of Hospitalisation) or other clincal trial drug treatment within 4 weeks prior to randomization, or radiotherapy within 2 weeks prior to randomization.
• Imaging demonstrating brain metastases (except patients who have completed whole brain radiotherapy or local therapy (such as surgery), have discontinued prednisone for at least 4 weeks prior to randomization, and have stable radiologically confirmed tumor lesions and no clinical symptoms of tumor during 4 weeks prior to randomization), metastases to meninges, or spinal cord compression.
• Thromboembolic events within 3 months prior to randomization (except patients with non-pulmonary Thromboembolism who do not require treatment or have been stably treated with anticoagulants for 14 days or longer prior to randomization).
• History of other neoplasm malignant within 5 years prior to randomization, except for neoplasm malignant cured after treatment.
• Having active autoimmune diseases requiring systemic treatment (i.e., immunologic modulator, corticosteroid, or Immunosuppression) within 2 years prior to randomization; replacement therapy (such as thyroid hormone, Insulin, or physiologic corticosteroid replacement therapy due to adrenal or pituitary insufficiency) is not considered systemic treatment.
• Known severe allergic reaction to any component in the investigational drug formula.

Other illness

• Tumor invades important surrounding structures (e.g., large blood vessels, trachea, etc.) with high risk of rupture and hemorrhage or airway fistula, or metastases to bone with high risk of paraplegia.

• Voluntarily participate in this study, have ICF signed after sufficient informed consent, and have good compliance.
• Age ≥ 18 years, male or female.
• ECOG PS 0 or 1.
• Expected survival period≥ 3 months.
• Patients with HER2 negative G/GEJ adenocarcinoma confirmed by histology/cytology.
• Patients who have received at least one prior line of systemic treatments and developed PD, and the previous treatment must include fluorouracil and platinum.
• Fresh or archival tumor tissue (blocks of formalin-fixed, paraffin-embedded \[FFPE\] tissue or unstained FFPE tumor tissue sections) must be available and comfirmed CLDN18.2 positivity by for central laboratory through immunohistochemistry (IHC) before randomization.
• Having ≥ 1 measurable lesion according to RECIST v1.1 (per investigator assessment).
• Any AEs and/or complications caused by previous therapies including surgery or radiotherapy have been adequately resolved to Grade 0 or 1 (per NCI-CTCAE v5.0 criteria) or have been stabilized in the judgment of investigators.