As part of its Single Technology Appraisal (STA) process, the UK National Institute for Health and Care Excellence (NICE) invited the manufacturer of ibrutinib (Janssen) to submit evidence on the clinical and cost effectiveness of ibrutinib for treating Waldenström's macroglobulinaemia (WM). The School of Health and Related Research Technology Assessment Group at the University of Sheffield was commissioned to act as the independent Evidence Review Group (ERG). The ERG produced a critical review of the evidence for the clinical and cost effectiveness of ibrutinib based on the company's submission to NICE. The clinical evidence was derived from one phase II, single-arm, open-label study of ibrutinib in adult patients with WM who had received at least one prior therapy (Study 1118E) and an indirect comparison using a matched cohort from a retrospective European chart review of patients receiving various treatments for WM. The indirect comparison suggested a hazard ratio for progression-free survival (PFS) of 0.25 (95% confidence interval 0.11-0.57). The ERG had concerns regarding the high risk of bias in Study 1118E, the limited generalisability of the study, and the absence of randomised controlled trial evidence. The company's Markov model assessed the cost effectiveness of ibrutinib versus rituximab/chemotherapy for patients with relapsed/refractory (R/R) WM from the perspective of the National Health Service (NHS) and Personal Social Services (PSS) over a lifetime horizon. Based on the company's original Patient Access Scheme (PAS), the company's probabilistic model generated an incremental cost-effectiveness ratio (ICER) for ibrutinib versus rituximab/chemotherapy of £58,905 per quality-adjusted life-year (QALY) gained. Following a critique of the model, the ERG's preferred analysis, which corrected cost errors and used the observed mortality rate from Study 1118E, generated a probabilistic ICER of £61,219 per QALY gained. Based on this amended model, additional exploratory analyses produced ICERs for ibrutinib that were > £60,000 per QALY gained. Subsequently, the company offered to provide ibrutinib at a price that resulted in ibrutinib being cost effective within the Cancer Drugs Fund (CDF). The Committee recommended ibrutinib for use in the CDF as an option for treating WM in adults who have had at least one prior therapy, only if the conditions in the managed access agreement for ibrutinib are followed.