Clinical Study on the Efficacy and Safety of LM-302 Injection Combined With Tislelizumab and Tislelizumab Combined Chemotherapy for the Treatment of Gastric or Gastroesophageal Junction Adenocarcinoma.

Inclusion Criteria: * Willing and able to comply with the study's visit schedule, treatment plan, laboratory tests, and other research procedures. * Age ≥ 18 years. * Histologically or cytologically confirmed adenocarcinoma of the stomach or gastroesophageal junction. * For locally advanced unresectable or metastatic adenocarcinoma of the stomach or gastroesophageal junction that has not previously received any systemic treatment: * Patients who have previously received radical neoadjuvant chemotherapy or adjuvant chemotherapy (radiotherapy) based on a platinum-based combination chemotherapy regimen and have not developed distant metastasis or local recurrence within 6 months after completion of treatment can be included. * The calculation of a 6-month interval is defined as recurrence within the same date range after 6 months. For example, if the end date of the last treatment is January 1, the 6-month period from that date refers to January 1 to July 1 (including July 1). Alternatively, if the end date of the last treatment is August 31, the 6-month period from that date refers to August 31 to February 28 (or February 29 in leap years). * Archived specimens or fresh tumor tissue specimens from ≤3 years ago must be provided for CLDN18.2 and PD-L1 testing (PD-L1 results are not a condition for enrollment). When multiple samples are present, the most recent accessible and qualified sample must be provided. After confirmation by the central laboratory, tumor tissue with p…