Fixed-duration pirtobrutinib plus venetoclax–rituximab versus venetoclax–rituximab for patients with previously treated chronic lymphocytic leukaemia or small lymphocytic lymphoma (BRUIN CLL-322): an open-label, multicentre, randomised, controlled, phase 3 trial

BACKGROUND: Venetoclax-rituximab (VR) following covalent Bruton tyrosine kinase (BTK) inhibitor therapy is the fixed-duration standard of care for patients with chronic lymphocytic leukaemia (including small lymphocytic lymphoma). Pirtobrutinib, a non-covalent BTK inhibitor, is approved for use after treatment with a covalent BTK inhibitor as a continuous therapy option. We aimed to evaluate the addition of pirtobrutinib to VR as a fixed-duration regimen in patients with relapsed or refractory chronic lymphocytic leukaemia. METHODS: This open-label, multicentre, randomised, controlled, phase 3 trial was conducted at 152 sites (comprising community hospitals and academic centres) across 22 countries. Eligible patients were aged 18 years or older, had a confirmed diagnosis of chronic lymphocytic leukaemia (including small lymphocytic lymphoma), and had previously been treated with at least one line of therapy that could include a covalent BTK inhibitor. Patients who had previously received a non-covalent BTK inhibitor, venetoclax, or another BCL2 inhibitor were not eligible. Enrolled patients were randomly assigned (1:1) using an interactive web-based randomisation system, stratified by del(17p) status and previous exposure to covalent BTK inhibitors, and assigned to receive either pirtobrutinib plus VR (PVR) or VR. Both groups received oral venetoclax (25 cycles) and intravenous rituximab (six cycles); the PVR group also received oral pirtobrutinib for 28 cycles, with a three-cycle pirtobrutinib-rituximab lead-in before venetoclax initiation. For this prespecified interim analysis, the primary endpoint was progression-free survival in the intention-to-treat population, assessed by a masked independent review committee (IRC) as per 2018 International Workshop on Chronic Lymphocytic Leukemia guidelines. Safety analyses were conducted in the safety population, defined as all randomly assigned patients who took at least one dose of any study treatment. All analyses were based on a data cutoff date of Feb 2, 2026. The trial is registered at ClinicalTrials.gov, NCT04965493, and is ongoing but no longer recruiting. FINDINGS: Between Oct 13, 2021, and Oct 28, 2024, 784 patients were screened, of whom 639 were randomly assigned: 321 to the PVR group and 318 to the VR group. The median age of patients was 68·0 years (IQR 60·0-74·0), of whom 439 (69%) were male and 200 (31%) were female. The median number of previous therapies was 2 (IQR 1-3); 510 (80%) of 639 patients had previous exposure to covalent BTK inhibitors, of whom 362 (71%) discontinued their most recent drug of this class owing to progressive disease. At a median follow-up of 27·3 months (IQR 19·5-38·7), PVR showed a significant improvement in IRC-assessed progression-free survival compared with VR (hazard ratio 0·547 [95% CI 0·400-0·748]; p=0·0001). The median 24-month progression-free survival rate was 87% (95% CI 82·3-90·4) in the PVR group versus 72% (65·7-77·0) in the VR group, and the median progression-free survival was not reached (IQR 31·7-not estimable) in the PVR group versus 39·7 months (21·5-50·0) in the VR group. This benefit was consistent across prespecified subgroups, including patients with previous exposure to covalent BTK inhibitors. The most frequent treatment-emergent adverse event of any grade in both groups was diarrhoea, reported in 106 (34%) of 316 patients in the PVR group and 110 (35%) of 311 patients in the VR group. The frequency of treatment-emergent adverse events of grade 3 or higher was similar in both groups (249 [79%] of 316 patients in the PVR group vs 227 [73%] of 311 patients in the VR group); the rate of tumour lysis syndrome of grade 3 or higher was lower in the PVR group (1%; three of 316) than in the VR group (4%; 12 of 311). Rates of atrial fibrillation or flutter of any grade were low (11 [3%] of 316 patients in the PVR group vs eight [3%] of 311 patients in the VR group). Rates of treatment discontinuation owing to treatment-emergent adverse events deemed as related to any of the study drugs were similar: 5% (17 of 316 patients) in the PVR group versus 5% (16 of 311 patients) in the VR group. There were five treatment-related deaths: one in the PVR group and four in the VR group. INTERPRETATION: In patients with previously treated chronic lymphocytic leukaemia, PVR showed significant improvement in progression-free survival compared with VR, with consistent results in patients who had previously received covalent BTK inhibitors and no new safety signals. To our knowledge, these results represent the first randomised phase 3 evidence comparing a novel fixed-duration regimen to the current standard of VR in relapsed or refractory chronic lymphocytic leukaemia, supporting PVR as a potential new standard of care. FUNDING: Eli Lilly and Company.