Inclusion Criteria:  Males and females ≥ 21 years of age Eastern Cooperative Oncology Group (ECOG) Performance Status of 0 to 2.  Patients must meet the following clinical laboratory criteria within 21 days of starting treatment:  Absolute neutrophil count (ANC) ≥ 1,000/mm3 and platelet ≥ 50,000/mm3 Total bilirubin ≤ 1.5 x the upper limit of the normal range (ULN). Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) ≤ 3 x ULN of ≤ 5 ULN if involvement of the liver. Calculated creatinine clearance ≥ 30 mL/min or creatinine < 1.5 x ULN. Main tumour types: Non-small cell lung cancer (NSCLC), gastric cancer (GC), hepatocellular carcinoma (HCC) and nasopharyngeal carcinoma (NPC) or other metastatic solid tumours not for curative intent therapy; Treatment with single-agent Nivolumab. If patients have already started treatment on this regimen, they may still be eligible to enrol, provided they fulfil all other criteria and approval is sought by PI and Sponsor. Eligible for treatment with single-agent nivolumab based on co-investigator's assessment of fitness for immunotherapy (e.g. not on high dose corticosteroid therapy or uncontrolled auto-immune disorder)  Exclusion Criteria:  Patients who are lactating or pregnant. Patients with clinically significant hypersensitivity to one or more of the selected regimen's constituent drug(s) (e.g. patient's with clinically significant hypersensitivity to oxaliplatin may not be enrolled on the XELOX regimen, but may be allowed on the XELIRI regimen). Contraindication to any of the required concomitant drugs or supportive treatments. Any clinically significant medical disease or psychiatric condition that, in the co-investigator's opinion, may interfere with protocol adherence or a subject's ability to give informed consent. Major surgery within 28 days prior to start of the treatment, Active congestive heart failure (New York Heart Association [NYHA] Class III or IV), symptomatic ischaemia, or conduction abnormalities uncontrolled by conventional intervention. Myocardial infarction within 4 months prior to informed consent obtained.