Factors associated with response to rituximab in patients with immune thrombocytopenia.

Rituximab is a well-established treatment for adult immune thrombocytopenia (ITP), with ~60% initial response (IR) and 20%-30% long-term remissions. We conducted a register-based cohort study of 759 ITP patients in Sweden, Denmark, and Norway treated with rituximab (2009-2018) to identify factors associated with response. IR-platelet count ≥ 30 × 10⁹/L or ≥2-fold increase from baseline without bleeding and platelet-elevating therapy in the prior 8 weeks, assessed 3-6 months post-treatment-occurred in 66.3%. IR in non-pretreated patients (receiving rituximab as first-line therapy) was 65% and 67% in pretreated (second-line or later) patients. Response incidence rates were 1.67 (95% CI 1.32-2.08) and 1.77 (95% CI 1.60-1.95) per person-years, respectively. Median response duration was 5.4 years (interquartile range [IQR] 2.6; 7.4), and 1.9 (IQR 0.4; 5.4), respectively. Sustained response (SR)-platelet ≥ 30 × 10⁹/L without bleeding and platelet-elevating therapy after IR-was 53.3% at 2 years and 31.4% at 5 years. Across evaluated covariates, no clear associations with IR were observed, indicating similar short-term effectiveness across patient subgroups. Exploratory models identified inconsistent associations with comorbidity burden and corticosteroid co-administration in some strata. Achieving complete response (platelet ≥ 100 × 10⁹/L and absence of bleeding) at 6 months was the strongest predictor of SR at 2 years (risk ratio [RR] 3.87, 95% CI 2.95-5.12) and 5 years (RR 4.30; 95% CI 2.95-6.27). Of 83 patients re-treated after first relapse, 60% responded; among 19 re-treated after second relapse, 63% responded. Our findings confirm rituximab response rates in ITP and highlight complete IR as the strongest predictor of long-term outcomes.