The Phase Ib VenObi CNS Study: Chemotherapy-Free Treatment with Venetoclax and Obinutuzumab for Relapsed/Refractory Primary Large B-Cell Lymphoma of the Central Nervous System

BACKGROUND/OBJECTIVES: Relapsed and refractory (rr) primary large B-cell lymphoma of the central nervous system (PCNSL) has a dismal prognosis, and the standard of care is not established. The most common genetic imbalance includes the B-cell lymphoma 2 (BCL-2) locus. METHODS: We planned a bi-centric phase Ib dose-escalation study with the chemotherapy-free combination of the BCL-2 inhibitor venetoclax and CD20 antibody obinutuzumab for rrPCNSL patients in Germany. The intended treatment consisted of 6 cycles of fixed-dose obinutuzumab at 1000 mg intravenously every 3 weeks, and an oral daily dose of 600, 800, or 1000 mg venetoclax, depending on the planned dosing group, followed by a 12-month venetoclax maintenance period. The primary endpoint was the pharmacokinetics of venetoclax and obinutuzumab in cerebrospinal fluid (CSF). RESULTS: This study was prematurely terminated after registration of 5/15 (33%) patients in dosing group 1 (600 mg oral daily dose of venetoclax) between May 2020 and November 2021. The mean ratio of the concentration of venetoclax in CSF over peripheral blood was 0.55% (±0.28 standard deviation (SD)) and 0.25% (±0.23 SD) for obinutuzumab. Two of five patients achieved complete remission, and each one patient achieved partial remission and stable disease as best response. The median duration of response was 6.5 months (range 0.7-47). CONCLUSIONS: Venetoclax and obinutuzumab can penetrate into the central nervous system, but the CSF concentration did not correlate with the outcome. The combination is feasible, tolerable, and may lead to durable responses in selected rrPCNSL patients.