Kaplan-Meier analysis of the time to relapse for 16 patients treated with rituximab and 21 patients not treated with rituximab for their initial episode of TTP. Two patients relapsed after rituximab treatment at 2.5 and 9.9 years. Nine patients who did not receive rituximab relapsed at 0.4 to 5.9 years (median, 3.1 years). Censored patients who had not relapsed at the time of their last follow-up are indicated by hash marks. Two patients not treated with rituximab and who had not relapsed died at 16 and 30 months; their deaths were related to preexisting systemic lupus erythematosus. Hash marks do not discriminate between 2 patients treated with rituximab who had the same duration of follow-up (1.5 years) and 2 patients not treated with rituximab who had the same duration of follow-up (3.8 years). The difference was significantly different (P = .009, calculated to account for the 2 competing events of death).⁶