Adjusting for treatment crossover in the MAVORIC trial: survival in advanced mycosis fungoides and Sézary syndrome.

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.