Inclusion Criteria:
* 1\. Capable of giving signed informed consent. 2. Male and/or Female, Age ≥ 18 years at the time of screening. 3. Histologically documented gastric or gastroesophageal junction adenocarcinoma with resectable disease, GEJC includes Siewert\* type 2 and 3 tumour and Siewert\* type 1 tumour.
1. Per the judgment of the Investigator, participants must be medically fit for treatment with neoadjuvant FLOT therapy prior to radical surgery.
2. At screening, complete surgical resection of the primary GC/GEJC must be deemed achievable, as assessed by a multidisciplinary evaluation, which must include a board certified GI surgeon.
3. No prior anti-cancer therapy (eg, chemotherapy, radiation therapy, or chemoradiation therapy) for the current malignancy.
4\. ECOG PS of 0 or 1 with no deterioration over the previous 2 weeks prior to baseline at screening and prior to randomization.
5\. Adequate organ and marrow function as defined below:
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1. Haemoglobin ≥ 9.0 g/dL
2. Absolute neutrophil count ≥ 1.5 × 109/L
3. Platelet count ≥ 100 × 109/L
4. Serum bilirubin ≤ 1.5 ×ULN. This will not apply to participants with confirmed Gilbert's syndrome, who will be allowed in consultation with their physician.
5. ALT and AST ≤ 2.5 × ULN
6. Measured CL \> 50 mL/min or Calculated CL \> 50 mL/min as determined by Cockcroft-Gault (using actual body weight) 6. Must have a life expectancy of at least 24 weeks. 7. Body weight \> 30 kg at enrolment and randomization. 8. Meeting tumour sample requirements (at screening) to confirm PD-L1 status.
Exclusion Criteria:
* -1. Participants with peritoneal dissemination (including tumour cells in peritoneal fluid) or distant metastasis.
2\. Participants with adenosquamous cell carcinoma, squamous cell carcinoma, or GI stromal tumour.
3\. History of allogeneic organ transplantation. 4. Active or prior documented autoimmune or inflammatory disorders (including inflammatory bowel disease \[eg, colitis or Crohn's disease\], systemic lupus erythematosus, sarcoidosis, granulomatosis with polyangiitis, Graves' disease, rheumatoid arthritis, hypophysitis, uveitis, etc), autoimmune pneumonitis, and autoimmune myocarditis.
5\. Uncontrolled intercurrent illness that would limit compliance with study requirement, substantially increase risk of incurring AEs or compromise the ability of the patient to give written informed consent.
6\. History of another primary malignancy except for
(a) Malignancy treated with curative intent and with no known active disease ≥ 2 years before the first dose of study intervention and of low potential risk for recurrence (b) Adequately treated non-melanoma skin cancer or lentigo maligna without evidence of disease (c) Adequately treated carcinoma in situ without evidence of disease 7. History of active primary immunodeficiency. 8. Active infection including tuberculosis (clinical evaluation that includes clinical history, physical examination and radiographic findings, and tuberculosis testing in line with local practice) and HIV verified by positive HIV-1 or HIV-2 antibodies.
9\. Mean QTc ≥ 470 ms calculated from 3 ECGs (within 15 minutes at 5 minutes apart).
10\. Known allergy or hypersensitivity to any of the study interventions or any of the study intervention excipients.
