A Decade of Ibrutinib for CLL with and without TP53 Aberration: Final Report on an Investigator-Sponsored Phase 2 Study Available to Purchase

• At 10-years of follow-up, single-agent ibrutinib maintained efficacy in CLL; median PFS was 7.2 years; median OS was not reached.

• After a median of 5 years on ibrutinib, 13 (15.5%) of 84 patients had undetectable MRD that was durable, even after drug discontinuation.

BTK inhibitors improve outcomes for patients with chronic lymphocytic leukemia (CLL). Long-term data with continuous therapy are limited. With a median follow-up of 10.0 years, we report final results on 84 patients with TP53 aberrations (del(17p) or TP53 mutation) or ≥65 years of age treated with 420mg of single-agent ibrutinib daily until progression or unacceptable toxicity. 52 (61.9%) patients were previously untreated, 56 (66.7%) had unmutated IGHV, and 53 (63.1%) had TP53 aberrations, including 34 who were treatment-naive. As of July 31, 2024, 9 (10.7%) patients continued ibrutinib, 39 (46.4%) discontinued ibrutinib for progressive disease, 31 (36.9%) for adverse events, and 5 (5.9%) withdrew consent. The median progression-free survival (PFS) was 7.2 years; median overall survival (OS) was not reached. In patients with and without TP53 aberrations, median PFS was 5.6 years and not reached, and 10-year OS was 51.3% and 75.3%, respectively. The estimated 10-year PFS and OS for patients with TP53-aberrant CLL treated in first line was 38.6% and 65.7%, respectively. Minimal residual disease (MRD) was quantified by peripheral blood flow cytometry annually. Undetectable MRD (at 10-4) was achieved in 13 (15.5%) patients after a median of 5 years. Twelve patients maintained uMRD, the longest observation ongoing at 8.0 years. Seventeen (42.5%) patients with best response of high MRD (>10-2) remained progression-free for over 5 years. These results highlight durable benefits and deepening responses with ibrutinib, including in high-risk CLL. Whether patients maintaining uMRD for years can safely discontinue therapy should be assessed prospectively. Clinicaltrials.gov: NCT01500733.