Safety and tolerability of ibrutinib monotherapy in Japanese patients with relapsed/refractory B cell malignancies

In this phase I dose-escalation study we evaluated the safety, tolerability, pharmacokinetics, and antitumor activity of ibrutinib, an oral covalent inhibitor of Bruton’s tyrosine kinase (BTK, in Japanese patients with relapsed/refractory B cell malignancies (RRBCM). Fifteen patients aged 42–78 years were enrolled to one of three cohorts. Cohort 1 (n = 3) consisted of two phases, a single-dose (140 and 280 mg) phase and a multiple-dose (420 mg) phase of ibrutinib; cohort 2 (n = 6) included multiple doses of ibrutinib 560 mg; and cohort 3 (n = 6) included only patients with chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) dosed at ibrutinib 420 mg. One patient (CLL/SLL cohort) experienced grade 3 pneumonia and sepsis, which were considered dose-limiting toxicities. No deaths were reported. The most common (≥ 20 % patients) adverse events were neutropenia, anemia, nasopharyngitis, increased bilirubin, and rash. Dose-dependent increase in maximum plasma concentration and area under the concentration from 0 to the last quantifiable time was observed, while time to reach maximum plasma concentration and elimination half-life was similar between doses. The overall response rate was 73.3 % (11/15) for all cohorts combined. Overall, ibrutinib (420 and 560 mg) was tolerable with acceptable safety profiles and effective for Japanese patients with RRBCM including CLL/SLL. Clinical trial registration: NCT01704963.