The aim of this study is to test the efficacy and safety of immunotherapy plus chemotherapy on people with a relatively rare type of gastric cancer. Participants will take the anti-PD-1 inhibitor (Tislelizumab) and platinum-based chemotherapy (oxaliplatin + capecitabine or oxaliplatin + S-1) in a 3-week cycle, followed by a radical operation after 6 cycles.

Inclusion Criteria:

• Histologically confirmed gastric adenocarcinoma,cT1-2N+M0 or cT3-4NanyM0;

• Males or females, aged 18-70 years;

• Gastroscopy and abdominal computed tomography (CT) scan-confirmed typical scirrhous gastric cancer (borrmann type 4) or large type 3 (over 8 cm);

• No peritoneal metastasis confirmed by laparoscopic exploration and with cytological examination of peritoneal washing of the Douglas pouch;

• ECOG performance status 0 or 1;

• Sufficient organ function:

  • white blood cell count > 4*10^9/L, neutrophil cell count > 1.5*10^9/L, hemoglobin > 90 g/L, platelet count > 100*10^9 /L
  • Serum bilirubin ≤ 1.5×upper limit of normal (ULN), AST, ALT ≤ 2.5×ULN
  • Creatinine ≤ 1.5 ×ULN or serum clearance > 60 ml/min
  • INR and aPTT ≤ 1.5 × ULN, only for subjects not receiving anticoagulant therapy;Subjects undergoing coagulation therapy should use a stable dose

• No prior anti-tumor therapy;

• Have signed informed consent before the beginning of treatment.

Exclusion Criteria:

• History of another malignancy within the last five years;
• Previous cytotoxic chemotherapy, radiotherapy or immunotherapy
• Unable to take drugs orally
• Allergic to to any drug of the study regimen;
• Women who are pregnant or breastfeeding or may be pregnant