A Phase II Study Assessing Long-term Response to Ibrutinib Monotherapy in Recurrent or Refractory CNS Lymphoma

Purpose: Ibrutinib is a first-in-class inhibitor of Bruton tyrosine kinase. We previously reported the safety and short-term antitumor activity of ibrutinib in 20 patients with relapsed or refractory (r/r) primary central nervous system (CNS) lymphoma (PCNSL) or secondary CNS lymphoma (SCNSL).Patients and Methods: We enrolled 26 additional patients with r/r PCNSL/SCNSL into the dose-expansion cohort of the trial into a combined cohort of 46 patients (31 with PCNSL and 15 with SCNSL). Patients received ibrutinib at 560 or 840 mg daily in the dose-escalation cohort and ibrutinib at 840 mg daily in the expansion cohort. The median follow-up was 49.9 and 62.1 months for patients with PCNSL and SCNSL, respectively. We sequenced DNA from available tumor biopsies and cerebrospinal fluid collected before and during ibrutinib therapy.Results: Tumor responses were observed in 23/31 (74%) patients with PCNSL and 9/15 (60%) patients with SCNSL, including 12 complete responses in PCNSL and 7 in SCNSL. The median progression-free survival (PFS) for PCNSL was 4.5 months [95% confidence interval (CI), 2.8-9.2] with 1-year PFS at 23.7% (95% CI, 12.4%-45.1%). The median duration of response in the 23 PCNSL responders was 5.5 months. The median PFS in SCNSL was 5.3 months (95% CI, 1.3-14.5) with a median duration of response of 8.7 months for the 9 responders. Exploratory biomarker analysis suggests that mutations in TBL1XR1 may be associated with a long-term response to ibrutinib in PCNSL (P = 0.0075). Clearance of ctDNA from cerebrospinal fluid was associated with complete and long-term ibrutinib responses.Conclusions: Our study confirms single-agent activity of ibrutinib in r/r CNS lymphoma and identifies molecular determinants of response based on long-term follow-up.