Efficacy and Safety of AK112 Combined Chemotherapy as Neoadjuvant Treatment for Signet Ring Cell-containing G/GEJ Adenocarcinoma

Study Overview The primary objective of this clinical trial is to evaluate the efficacy and safety of AK112 in combination with chemotherapy as a neoadjuvant treatment for patients with locally advanced, resectable gastric or gastroesophageal junction (G/GEJ) adenocarcinoma containing signet ring cells. Key Research Questions 1. Does neoadjuvant treatment with AK112 plus chemotherapy improve the pathological complete response (pCR) rate compared to chemotherapy alone in patients with locally advanced G/GEJ adenocarcinoma with signet ring cells? 2. What are the safety profile and additional efficacy outcomes of AK112 combined with chemotherapy in this patient population? To answer these questions, the study will compare the combination of AK112 and chemotherapy with chemotherapy alone. Participant Procedures Eligible participants will: 1. Receive standard-dose AK112 in combination with chemotherapy every 3 weeks for a total of 4 cycles prior to surgery. 2. Undergo preoperative CT or MRI imaging within 3-4 weeks after the last treatment cycle to assess tumor response and evaluate eligibility for curative resection. 3. If no evidence of disease progression is observed and surgical evaluation is favorable, patients will undergo curative-intent gastrectomy within 6 weeks of completing neoadjuvant therapy (including oral agents, if any). 4. Postoperatively, adjuvant therapy will be administered at the investigator's discretion. Patients will be followed until disease recurrence or metastasis. 5. Attend clinic visits every 6 weeks during the neoadjuvant phase for evaluations and laboratory tests. 6. Maintain a symptom diary throughout the study period. 7. Undergo follow-up assessments every 3 months, starting from the first dose of study medication until 30 days after the last dose or the initiation of a new anti-tumor therapy. Optional Imaging Substudy FAPI-PET/CT imaging will be explored as an optional diagnostic modality. Participation in this substudy will requ