Lower doses in cycles 2 and 3 reduce inhibition of platelet function by ibrutinib. Platelet aggregation in platelet-rich plasma isolated from patients before and during ibrutinib therapy was measured by light transmission aggregometry after stimulation with 20 μM ADP in (A) patient 9 and (B) patients 8 and 9; or 1.5 mg/mL ristocetin in (C) patient 9 and (D) patients 8 and 9 before the start of therapy and on D1 24 hours of each cycle.