Factors associated with response to rituximab in patients with immune thrombocytopenia

Abstract 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.