Background: Relative overall survival (OS) estimates reported in the MAVORIC trial are potentially confounded by a high proportion of patients randomized to vorinostat switching to mogamulizumab; furthermore, vorinostat is not used in clinical practice in the UK. Methods: Three methods were considered for crossover adjustment. Survival post-crossover adjustment was compared with data from the Hospital Episode Statistics (HES) to contextualize estimates. Results: Following adjustment, the OS hazard ratio for mogamulizumab versus vorinostat was 0.42 (95% CI: 0.18, 0.98) using the method considered most appropriate based on an assessment of assumptions and comparison with HES. Conclusions: OS of mogamulizumab relative to vorinostat may be underestimated in MAVORIC due to the presence of crossover. The HES database was used to validate this adjustment.

Aim: This study assessed the cost–utility of mogamulizumab, a novel monoclonal antibody, versus established clinical management (ECM) in UK patients in previously treated advanced mycosis fungoides (MF)/Sézary syndrome (SS). Materials & methods: Lifetime partitioned survival model based on overall survival, next treatment-free survival and the use of allogeneic stem cell transplant was developed. Inputs were from the pivotal MAVORIC trial, real-world evidence and published literature. Extensive sensitivity analyses were conducted. Results: Discounted incremental quality-adjusted life years (QALYs), costs and incremental cost–effectiveness ratio were 3.08, £86,998 and £28,233. Results were most sensitive to the survival extrapolations, utilities and costs after loss of disease control. Conclusion: Mogamulizumab is a cost-effective alternative to ECM in UK patients with previously treated advanced MF/SS.