Sample size calculation
Enrolment continued until at least 160 patients were randomised. This sample size was calculated based on a goal of achieving 90% power under the alternative hypothesis of a HR of 0.42 at the 5% significance level with 58 observed relapses. This assumed a drop-out rate of 5% at 24 months and a relapse-free rate of 75% and 50% at 48 months in the rituximab and azathioprine arms, respectively.