RecruitingDrug trialRituximab and Ibrutinib (RI) Versus Dexamethasone, Rituximab and Cyclophosphamide (DRC) as Initial Therapy for Waldenström's MacroglobulinaemiaWaldenström's macroglobulinaemia (WM) is a rare type of slow growing lymphoma. It develops when white blood cells grow abnormally. Typically a disease of the elderly, the median age of presentation is \>70 years and the current treatment for WM is unsatisfactory, with incomplete responses and inevitable recurrence. Therefore there is a need to find alternative treatments that are more effective, leading to lasting responses and improved quality of life. The RAINBOW study is a phase 2-3 trial assessing 'chemotherapy free' treatment as primary therapy for WM which can potentially improve response outcome, durability and importantly, reduce toxicity for WM patients. This approach will be done using the drug Ibrutinib, which in combination with rituximab (RI) will be the experimental arm. As there is no agreed standard on first-line therapy for WM, the control arm is the current treatment based on the most recently published clinical trial results. The control arm consists of rituximab, cyclophosphamide and dexamethasone (DCR), and is widely recommended by international consensus as appropriate treatment for first-line therapy for WM. In this study, 148 adults (aged ≥ 18 years) with treatment naïve WM will be randomised on a 1:1 ratio to either the treatment or control arm. Randomised treatment lasts for a maximum of 6 cycles and response will be assessed following 3 cycles of treatment and completion of randomised treatment at approximately 24 weeks after commencing treatment. RI patients may then have up to 5 years of Ibrutinib monotherapy. Patients will be seen regularly during treatment and then every 3 months for 5 years after treatment discontinuation. Patients will enter annual follow up for survival until the end of trial (including progressed patients). The study will be conducted at NHS hospitals and is expected to last 9 years and 6 months.