Zimberelimab Anti-PD1 +/- Domvanalimab in Resectable Mmrd Gastric Cancer

Inclusion criteria * Age: ≥18 years * Histologically confirmed gastric or gastro-oesophageal junctional (GOJ) adenocarcinoma (inclusive of Siewert-stein classification type I-III (62)) * MMRd/MSI-H. There are three different methods validated for detection (63) : * Immunohistochemistry (IHC) staining for expression of MMR proteins (MLH1, MSH2, PMS2 and MSH6), MMRd defined as loss of function or one or more of these proteins. * Polymerase chain reaction (PCR) amplification of microsatellite sequences * Next-generation sequencing (NGS) for detection of MSI * Stage II-IIIB: TNM T2-T4, N0-N3, M0 * Absence of distant metastatic disease on CT scan + PET CT + staging laparoscopy prior to study entry. * MDT determined suitable for surgery and MDT believes an R0 resection is achievable after neo-adjuvant therapy (resectable disease) * No prior anti-cancer therapy for gastric / GOJ adenocarcinoma * ECOG performance status 0-2 Laboratory parameters • Adequate haematologic and end-organ function defined by the following laboratory test results: Haematology: Absolute neutrophil count \> 1.5 x 109/L Platelets \> 100 x 109/L Haemoglobin \> 90 x 109/L (can be post-transfusion) Biochemistry: Serum Creatinine Clearance \>50ml/min (calculated using Cockcroft-Gault formula Appendix X) Liver function: Bilirubin within normal limits ALT/AST ≤2.5x ULN Coagulation profile (for patients not receiving therapeutic anticoagulation): International Normalised Ratio (INR) \< 1.5 Activated Pr…