Immune thrombocytopenia (ITP) is an autoimmune disease associated with autoantibodymediated platelet destruction and impaired platelet production, resulting in thrombocytopenia and a predisposition to bleeding. The ongoing, global phase 1/2 study showed that rilzabrutinib, a Bruton tyrosine kinase inhibitor specifically developed to treat autoimmune disorders, could be an efficacious and well-tolerated treatment for ITP. Clinical activity, durability of response, and safety were evaluated in 16 responding patients who continued rilzabrutinib 400 mg twice daily in the long-term extension (LTE) study. At LTE entry, the median platelet count was 87 x 10(9)/L in all patients, 68 x 10(9)/L in those who had rilzabrutinib monotherapy (n = 5), and 156 x 10(9)/L in patients who received concomitant ITP medication (thrombopoietin-receptor agonists and/or corticosteroids, n = 11). At a median duration of treatment of 478 days (range, 303-764), 11 of 16 patients (69%) continued to receive rilzabrutinib. A platelet count of >= 50 x 109/L was reported in 93% of patients for more than half of their monthly visits. The median percentage of LTE weeks with platelet counts >= 30 x 10(9)/L and >= 50 x 10(9)/L was 100% and 88%, respectively. Five patients discontinued concomitant ITP therapy and maintained median platelet counts of 106 x 10(9)/L at 3 to 6 months after stopping concomitant ITP therapy. Adverse events related to treatment were grade 1 or 2 and transient, with no bleeding, thrombotic, or serious adverse events. With continued rilzabrutinib treatment in the LTE, platelet responses were durable and stable over time with no new safety signals.