Single-Agent Ibrutinib in Recurrent/Refractory Central Nervous System Lymphoma

BACKGROUND: Primary Central Nervous System Lymphoma (PCNSL) is an aggressive primary brain tumor with median progression free survival (PFS) after upfront methotrexate-based chemotherapy of 2-3 years. Outcome and treatment options are poor for recurrent/refractory (r/r) disease. Response rates (ORR) range between 30-60% with a PFS of 2-5 months. Ibrutinib has shown promising clinical response in Mantel cell lymphoma, CLL, and Waldenström. This trial investigates Ibrutinib in patients with r/r PCNSL and SCNSL.

METHODS: Eligible patients had r/r PCNSL or Secondary CNS Lymphoma (SCNSL), age≥18, ECOG≤2, normal end-organ function, and unrestricted number of CNS directed prior therapies. In patients with SCNSL disease, systemic disease needed to be absent.

RESULTS: Twenty patients were enrolled (3 at 560 mg; 17 at 840 mg). Median age was 69 (range 21-85); 12 were women. Median ECOG was 1 (0: 2, 1: 12, 2: 6). 65% had PCNSL and 35% SCNSL; 70% had recurrent disease. Eleven had parenchymal disease, 3 isolated cerebrospinal fluid (CSF) involvement and 6 both. Five grade 4 adverse events were observed in 4 patients (lymphopenia (2), sepsis (1), neutropenia (2)). Ten patients developed grade 3 toxicities, including lymphopenia in 3 patients, thrombocytopenia in 2, hyperglycemia in 2, lung infection in 2, neutropenia in 1, urinary tract infection in 1, colitis in 1, and fungal encephalitis in 1. The most common toxicities were hyperglycemia, anemia, and thrombocytopenia. After a median follow-up of 193 days, 19/20 patients were evaluated for response: 8 CR, 7 PR, 1 SD and 3 PD; 75% (15/20) ORR. The median PFS is 7.29 months (95% CI: 3.80-15.43 months (longest: 15.3 months)). The mean Ibrutinib concentration in the CSF 2h post administration at day 1 and 29 is 1.75 ng/mL (3.97 nM) and 2.51 ng/mL (5.6 nM) which is above the IC50 (1nM) required in vitro to reduce growth of lymphoma cells.An additional treatment arm has been added to the trial which will evaluate adverse events of the combination of ibrutinib and high-dose methotrexate chemotherapy. Enrollment into the combination arm is ongoing and updates will be presented at the meeting.

CONCLUSION: Patients with CNS lymphoma tolerate Ibrutinib with manageable adverse events. Drug concentrations in CSF are higher at steady state (day 29) and meaningful CSF concentrations are reached. Clinical response was seen in 75% of CNS lymphoma patients. A combination arm will assess the adverse events of ibrutinib in combination with high-dose methotrexate chemotherapy.