Statistical methods

Categorical variables were expressed as number (%) and continuous variables as median (range).

The chi‐square test was used for bivariate comparisons of categorical variables. Survival curves with 95% confidence intervals (CIs) were computed using the Kaplan–Meier method. In accordance to statistical methodology no CI was computed for the standard population, as the standard population was based on actual national historical death rates. Overlapping CI intervals were used to examine survival disparities between different cohorts of the study population and the survival of the derived standard population. Survival at different EFS milestones (12 and 24 months) was calculated (including only patients achieving the specified milestone in the analysis). A standardised mortality ratio (SMR) using observed to expected deaths was calculated for 1 and 5 years after achieving the landmark time‐point. Cox proportional hazard was used for multivariate analysis including prognostic parameters based on the IPI score. A two‐sided P ≤ 0·05 was regarded as the cut‐off for statistically significant results in comparisons between groups.

Statistical analyses were performed using the R statistical program version 3.4.3 (R Foundation for Statistical Computing, Vienna, Austria; www.r‐project.org). The study was approved by the local Review Board in Uppsala, Sweden.