Australasian Leukaemia & Lymphoma Group NHL32 Block PCNSL: An Open Label Phase II Study of Pembrolizumab Following Chemoimmunotherapy for Newly Diagnosed Primary Central Nervous System Lymphoma - Trial in Progress
Authors: Tatarczuch Maciej , Keane Colm , Brown Christina , Giri Pratyush , Cull Gavin , Lasica Masa , Shuttleworth Charles , Wight Joel , Tabesh Marjan , Butcher Belinda E , Lee Sze Ting , Hawkes Eliza A. , Gregory Gareth P. 
Published: December 2024

Background:
Diffuse Large B-cell lymphoma of the Central Nervous System (DLBCL of the CNS), or Primary CNS Lymphoma (PCNSL), is an aggressive disease of predominantly older patients with a median age at diagnosis of 67 and increasing incidence in those over 70. The current standard of care is intensive chemoimmunotherapy (CIT) containing high-dose methotrexate (MTX) and cytarabine (Ara-C), such as MATRix (MTX, Ara-C, thiotepa, rituximab) or R-MPV/Ara-C (rituximab, MTX, procarbazine, vincristine followed by Ara-C), followed by consolidation with either autologous stem cell transplantation (ASCT) or whole brain radiotherapy (WBRT) for suitable patients. While favorable responses can be achieved (2-year PFS: 57-69%, 2-year OS: 71-81%), questions remain regarding the benefit of either consolidative strategy, particularly in patients who achieve a complete response to induction CIT. Sparing patients from WBRT-related cognitive impairment and the well-described morbidity and mortality of ASCT continues to be a priority, as are novel approaches for those not eligible for either strategy due to age or comorbidities. Genomic interrogation of PCNSL has demonstrated copy number alterations and translocations affecting chromosome 9p24.1 (encoding loci for PD-L1 and PD-L2), providing therapeutic rationale for treatment with PD-1 inhibition. Furthermore, case series and phase 2 studies have demonstrated that PD-1 inhibition can lead to clinical and radiological responses in the relapsed setting. NHL32 is a national cooperative group trial in progress examining an alternative consolidation strategy with PD-1 blockade with the anticipated outcome of improved long-term disease control and reduction in late neurocognitive complications or morbidity associated with WBRT and ASCT respectively.
Method:
ALLG NHL32 (BLOCK PCNSL) [ACTRN12619000518167] is a phase II, single arm, open-label trial of CIT followed by pembrolizumab maintenance, which has been designed using Fleming-A'Hern early phase principles. The trial is open to recruitment across Australia. Approximately 45 patients with newly diagnosed PCNSL will be enrolled. Eligible patients receive induction CIT, either R-MPV/Ara-C or MATRix as per investigator choice. Patients who achieve stable disease or better and adequate resolution of toxicity (i.e. grade &lt;3) after induction CIT will proceed to maintenance pembrolizumab (200mg) administered intravenously every 21 days for 35 cycles or until disease progression. Eligible patients are adults (&gt;18 years) with treatment-naïve histologically confirmed DLBCL of the CNS, ECOG performance status 0-1 (or 2 if due to neurological deficit), and adequate organ function to receive induction CIT. Key exclusion criteria include presence of active autoimmune disease and previous treatment with checkpoint blockade or CAR-T therapy.
The primary endpoint is 1-year progression free-survival (PFS) from cycle 1, day 1 of CIT (intent-to-treat population) as estimated using the Kaplan-Meier method. The secondary endpoints include 2-year PFS, 2-year OS, PFS with subgroup analysis according to induction CIT and response endpoints. Adverse event reporting during CIT phase will be limited to grade &gt;3 events. The safety analysis of adverse events occurring during the pembrolizumab phase will be descriptive, with the number of patients experiencing the event and percentage presented. Exploratory endpoints include describing the utility of PET/MRI assessment for treatment response and biomarkers such as molecular profiling of tumour-tissue, gene expression profiling for immune gene signatures and cell-of-origin, PD-1/PD-L1 immunohistochemistry, 9p24 FISH and circulating tumour DNA (plasma and CSF).