Temozolomide + Nivolumab in MGMT Methylated Oesophagogastric Cancer

INCLUSION CRITERIA * Patients ≥ 18 years of age * Pathologically confirmed advanced unresectable or metastatic OGA * MGMT methylation on archival tissue * Mismatch repair proficient (MSI-normal or MMR intact) * Previously treated with at least 3 months of platinum and fluoropyrimidine based chemotherapy for advanced disease and without evidence of disease progression. * Measurable disease per RECIST 1.1. * Eastern Cooperative Oncology Group (ECOG) Performance Status of 0 or 1 * Can swallow TMZ capsules * Adequate organ function assessed within 7 days before randomization: * White blood cell count (WBC) \> 1.5 x 109/L * Absolute neutrophil count (ANC) \> 1.5 x 109/L * Platelets ≥ 100 x 109/L * Haemoglobin ≥ 90 g/L * Measured/calculated creatinine clearance ≥ 60 mL/min (according to Cockroft-Gault formula). * Total bilirubin within normal limits (if the patient has documented Gilbert's disease ≤ 1.5 x ULN or direct bilirubin ≤ 1.5 x ULN) * Aspartate transaminase (AST) and/or alanine transaminase (ALT) ≤ 1.5 x ULN * All toxicities (exception alopecia, and grade 2 fatigue, neuropathy and lack of appetite /nausea) attributed to prior anti-cancer therapy must have resolved to grade 1 (NCI CTCAE version 5.0) or baseline before administration of study drug. * Women of childbearing potential (WOCBP) may be included following a confirmed menstrual period and must have a negative serum or urine pregnancy test (minimum sensitivity 25 IU/L or equivalent units of human chor…