Inclusion Criteria: 1. General Inclusion Criteria 1. Males and females ≥ 21 years of age. 2. Eastern Cooperative Oncology Group (ECOG) Performance Status of 0 to 2. 3. Patients must meet the following clinical laboratory criteria within 21 days of starting treatment: 1. Absolute neutrophil count (ANC) ≥ 1,000/mm3 and platelet ≥ 50,000/mm3 2. Total bilirubin ≤ 1.5 x the upper limit of the normal range (ULN). Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) ≤ 3 x ULN or ≤ 5 ULN if involvement of the liver. 3. Calculated creatinine clearance ≥ 30mL/min or creatinine < 1.5 x ULN Exclusion Criteria: 2. General Exclusion Criteria 1. Patients who are lactating or pregnant. 2. Major surgery within 28 days prior to start of the treatment. 3. 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. 4. 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). 5. Contraindication to any of the required concomitant drugs or supportive treatments. 6. Any clinically significant medical disease or psychiatric condition that, in the investigator's opinion, may interfere with protocol adherence or a subject's ability to give informed consent. 3. Specific Recruitment Criteria for Cohort 1: Capecitabine in solid tumours i. Specific Inclusion Criteria 1. Metastatic solid tumours not for curative intent therapy; 2. Planned for treatment with the following chemotherapy regimens: XELOX, XELIRI or single agent capecitabine. 3. Patients must have raised tumour marker above upper limit of local laboratory normal (e.g. CEA, CA19-9). ii. Specific Exclusion Criteria Nil d. Specific Recruitment Criteria for Cohort 2: Ibrutinib in Waldenström macroglobulinaemia i. Specific Inclusion Criteria 1. Waldenström macroglobulinaemia (either newly diagnosed or relapsed) as defined by the World Health Organisation 2016 diagnostic criteria. 2. Immunofixation confirms immunoglobulin M paraprotein and total IgM > 2 x ULN. ii. Specific Exclusion Criteria 1. Systemic anti-lymphoma therapy within 3 weeks of enrolment. Steroids at a dose equivalent of prednisolone 30mg per day are allowed provided this is discontinued 72 hours prior to commencement of drug dosing on trial. 2. Need to withhold rituximab in view of the risk of IgM flare (applies to patients treated with rituximab-based regimens). 3. Platelet transfusion within 7 days of screening. 4. Granulocyte colony stimulating factor within 7 days of screening.