Efficacy and Safety of the Bruton's Tyrosine Kinase Inhibitor Zanubrutinib in Immune Thrombocytopenia

Abstract

Immune thrombocytopenia (ITP) is characterized by impaired platelet production and increased platelet destruction. Zanubrutinib is a highly selective next-generation Bruton tyrosine kinase (BTK) inhibitor that may reduce autoantibody production and reduce macrophage Fcγ receptor-mediated platelet destruction. In this single-arm, phase II study, we aimed to assess the efficacy and safety of zanubrutinib in corticosteroid-resistant or relapsed ITP. All patients received 80 mg zanubrutinib once daily for 6 weeks followed by a 20-week safety follow-up period. The primary endpoint was overall response (OR), defined as at least two consecutive platelet counts of at least 30 × 10⁹/L, at least a 2-fold increase in the baseline count, the absence of bleeding, and no need for rescue therapy at 4 weeks. The trial was registered with ClinicalTrials.gov, number NCT05279872. Between January 1, 2022 and October 30, 2022, 20 patients were enrolled. The median platelet count was 19 (10–25) × 10⁹/L at the time of enrollment. Participants had received a median of 4 (3–6) different therapies for ITP. Eleven (55%, 95% CI: 31.5%–76.9%) patients achieved an OR to the intervention. Two (10%) patients achieved a complete response. At the 6-month follow-up, a sustained response was achieved in seven (35.0%, 95% CI: 15.4%–59.2%) patients. There were no grade 4 or worse adverse events or treatment-related deaths. The most common adverse events were upper respiratory tract infection (in 25% of the patients). Zanubrutinib showed an encouraging response rate and tolerability, supporting its therapeutic potential for the treatment of ITP.