Time-Limited Venetoclax and Ibrutinib for Patients with Relapsed/Refractory Chronic Lymphocytic Leukemia (R/R CLL) Who Have Undetectable MRD - Primary Analysis from the Randomized Phase II Vision HO141 Trial

Background: For patients with Relapsed/Refractory Chronic Lymphocytic Leukemia (R/R CLL), targeted time-limited treatment options are warranted. Thus far, therapeutic options are based on a (one-size-fits-all) fixed treatment duration or treatment until progression independent of individualized responsiveness. Post-treatment minimal residual disease (MRD) predicts outcome for patients receiving venetoclax-based therapy.

Aim: To evaluate Progression-Free Survival (PFS) for patients with R/R CLL 12 months after MRD guided treatment cessation of venetoclax + ibrutinib (V+I) treatment (arm B) with the option to reinitiate V+I based on MRD reappearance.

Methods: Patients (BTK inhibitor naïve) received ibrutinib lead-in (420 mg daily) for two (28-day) cycles. Venetoclax ramp-up was initiated during cycle 3, reaching 400 mg daily at cycle 4 with continued V+I during cycle 4-15. Patients reaching at least partial remission (PR) and undetectable (u)MRD (<10 ^-4) in blood (PB) and bone marrow (BM, by central 8-color flow cytometry) at cycle 15 day 15 were randomized 1:2 between ibrutinib maintenance (arm A) or treatment cessation (arm B). Patients later becoming MRD positive (>10 ^-2) in arm B reinitiated V+I. MRD positive patients at cycle 15 remained on ibrutinib until progression.

Results: 225 patients were enrolled: median age 68 years (range 36-87), median CIRS score 2 (range 0-12), Binet stage B/C 84%, IGHV unmutated: 64%, TP53 aberrations (deletions and/or mutations): 24%. Planned treatment until randomization was completed by 194 (86%) patients, 8 patients went off protocol due to toxicity, 5 (2%) patients died during the first two cycles of ibrutinib lead-in (unknown cause, myocardial infarction, intracranial hemorrhage, Richter's transformation and tick-borne viral encephalitis), 15 patients went off protocol due to refusal to continue or other reasons and 3 patients progressed. At cycle 15, 81 (36%) patients achieved uMRD in both PB (112, 50%) and BM (84, 37%) and overall responses were 86%, of which 145 pts (64%) CR(i). Patients with uMRD were randomized to ibrutinib maintenance arm A (n 24 11%) or observation arm B (n 48 21%). Patients who did not achieve uMRD (n 125, 56%) continued ibrutinib maintenance without randomization while 5 patients went off protocol.

The primary endpoint of the trial was met; PFS was achieved for 47 (98%) of 48 patients randomized to observation arm B at 12 months after randomization (27 months after starting therapy). One patient died during observation due to myelodysplastic syndrome and 1 patient, without sign of progression, reinitiated per protocol due to MRD positivity. A similar proportion of uMRD patients randomized to ibrutinib maintenance (arm A) or observation (arm B) remained uMRD after 12 months (month 27 after treatment start); 75% and 71%, respectively; see figure. No difference in blood uMRD at cycle 15 was seen neither between TP53 aberrated/wildtype (uMRD: 46%, 52%) nor between IGHV unmutated/mutated patients (uMRD: 50%, 50%).

The most frequent adverse event (AE, only grade ≥2) was infections with 68 (30%) grade 2 and 62 (28%) grade ≥3 during the first 15 cycles, while 14 (58%) and 6 (12%) infections appeared after randomization in the treatment arm A and observation arm B, respectively. Atrial fibrillation was reported for 29 (13%) patients during the first 15 cycles, for 4 (3%) during ibrutinib maintenance (arm A + non-randomized) while no patients were reported with atrial fibrillation in arm B. Hypertension was reported for 23 (10%) patients during the first 15 cycles and for 10 (7%) patients during ibrutinib maintenance while no events were reported in arm B. One fatal bleeding event was reported in addition to 32 (14%) grade 2-3 bleeding events during the first 15 cycles; 12 (9%) grade 2-3 bleeding events were reported during ibrutinib maintenance, while no events were reported in arm B. Laboratory tumor lysis grades 2-3 was reported for 11 (5%) of patients.

Conclusion: MRD guided time-limited treatment with ibrutinib and venetoclax in the setting of R/R CLL is feasible and demonstrates a favorable benefit-risk profile. No new safety signals were detected. No patients progressed after treatment cessation while patients becoming MRD positive successfully reinitiated therapy, thus proving MRD-guided cessation and reinitiation of targeted therapy feasible in CLL.

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