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Introduction: Key characteristics of immune thrombocytopenia (ITP) include immune-mediated platelet destruction/impaired production, with resultant thrombocytopenia and increased bleeding risk. Durable response to current therapies remains an unmet need, particularly in the relapsed/refractory setting. Rilzabrutinib is the first oral, reversible, covalent inhibitor of Bruton tyrosine kinase designed to target immune-mediated pathways in ITP without inhibiting normal platelet aggregation. Initial phase I/II results in ITP demonstrated rapid and durable efficacy with rilzabrutinib that was well-tolerated at all dose levels, including the optimal 400 mg bid dose. Interim results on rilzabrutinib effects in patients with relapsed/refractory ITP were previously reported. Here we present long-term data from a larger group of patients who initiated rilzabrutinib at 400 mg bid and are continuing in the long-term extension (LTE) period. Method(s): This ongoing, global phase I/II study (NCT03395210) enrolled adult patients from 8 countries with relapsed or refractory ITP who previously responded to >=1 prior ITP therapy. Eligible patients with 2 baseline platelet counts of <30x10 9/L no less than 7 days apart in the 15 days before baseline received oral rilzabrutinib at starting doses of 200 or 400 mg QD, 300 or 400 mg bid for 24 weeks; intrapatient dose escalation was permitted to improve efficacy. Stable doses of concomitant corticosteroids and thrombopoietin receptor agonists were allowed for patients with inadequate platelet response. The primary endpoints were safety and achievement of >=2 consecutive platelet counts >=50x10 9/L and increased >=20x10 9/L from baseline without rescue medication. Responding patients could continue in the LTE period with rilzabrutinib at the optimal 400 mg bid dose. Result(s): As of June 1, 2021 in 60 patients, 45 patients initiated rilzabrutinib 400 mg bid and to date, 16 patients with durable, stable response proceeded to LTE at 400 mg bi