Safety and efficacy of rilzabrutinib vs placebo in adults with immune thrombocytopenia: the phase 3 LUNA3 study

Rilzabrutinib is a covalent, reversible BTK inhibitor with multiple mechanisms targeting key immune thrombocytopenia (ITP) disease pathophysiology. The phase 3 LUNA3 study in previously treated adults with persistent/chronic ITP evaluated oral rilzabrutinib 400 mg bid (n=133) vs placebo (n=69) for 24 weeks. At baseline overall, median age was 47 years (range, 18-80), 63% female, 7.7 year (range, 0.3-52.2) median duration of ITP, and 28% were splenectomized. Overall (N=202), 85 (64%) rilzabrutinib and 22 (32%) placebo patients achieved platelet response (≥50×109/L or 30×109/L-<50×109/L and doubled from baseline) during the first 12 weeks and were eligible to complete the double-blind period. The primary endpoint durable platelet response (platelet count ≥50×109/L for ≥two-thirds of ≥8 of the last 12 of 24 weeks without rescue therapy) was observed in 31 (23%) rilzabrutinib vs 0 placebo patients (P<0.0001). All secondary efficacy endpoints were significantly superior for rilzabrutinib (P<0.05). Median time to first platelet response was 15 d in rilzabrutinib responders. Rilzabrutinib significantly reduced rescue therapy use by 52% (P=0.0007) and improved week 25 bleeding scores (P=0.0006). Improved physical fatigue was sustained from week 13 (P=0.01) through 25 (P=0.0003). Treatment-related adverse events were mainly grade 1-2. One rilzabrutinib patient with multiple risk factors had serious treatment-related grade 3 peripheral embolism (lower left leg) and another died from unrelated pneumonia. Rilzabrutinib­­ in ITP patients who failed multiple previous therapies (splenectomy, TPO-RA, rituximab and/or fostamatinib) resulted in rapid and durable platelet response, reduced rescue medication use and bleeding, significantly improved physical fatigue, and showed favorable safety. NCT04562766; EudraCT 2020-002063-60