according to a phase 3 trial published in the New England Journal of Medicine.
The trial, dubbed GAIA–CLL13, “is a remarkable demonstration of the quality of fixed-duration therapies for younger, fit patients, and it challenges us to continue to work to develop therapeutic strategies that will ultimately cure patients with CLL,” two hematologic cancer specialists said in an accompanying editorial.
In short, “venetoclax-obinutuzumab and venetoclax-obinutuzumab-ibrutinib were superior to chemoimmunotherapy with respect to both the minimal residual disease end point and progression-free survival, but venetoclax-rituximab was not,” Jennifer Woyach, MD, of Ohio State University, Columbus, and John Byrd, MD, University of Cincinnati, said in their commentary.
Noting that randomized trials involving venetoclax combinations in fit CLL patients “have been lacking,” the investigators compared 6 cycles of chemoimmunotherapy (fludarabine-cyclophosphamide-rituximab or bendamustine-rituximab) with 12 cycles of venetoclax plus the anti-CD20 antibody rituximab, venetoclax plus the third generation anti-CD20 antibody obinutuzumab, and venetoclax combined with both obinutuzumab and the Bruton’s tyrosine kinase inhibitor ibrutinib in a novel triple-therapy regimen.
The 926 patients in the study were a mean of 61 years old and split about evenly among the four treatment arms. Ibrutinib was discontinued after two consecutive measurements if patients had undetectable minimal residual disease (uMRD). Subjects did not have TP53 aberrations, a marker of poor prognosis in CLL.
At 15 months, the percentage of patients with uMRD was significantly higher in the triple-therapy arm (92.2%) and the venetoclax-obinutuzumab group (86.5%) than in the chemoimmunotherapy group (52.0%), but there was no statistical difference with venetoclax-rituximab (57%, P = .32).
The three-year progression-free survival (PFS) was 90.5% in the triple-therapy arm versus 87.7% with venetoclax-obinutuzumab. The 3-year PFS with venetoclax-rituximab (80.8%) was again not statistically different than the 75.5% with chemoimmunotherapy (P = .18).
Not ready for prime time
The benefits of triple therapy and venetoclax-obinutuzumab held only in patients with unmutated IgVH. “The high efficacy of the fludarabine, cyclophosphamide, and rituximab regimen in young, fit patients with mutated IgVH may be difficult to improve on,” noted the investigators, led by Barbara Eichhorst, MD, a hematologic malignancy specialist at the University of Cologne (Germany).
Also, although triple-therapy results were impressive, some of the benefits “are neutralized by the need for dose reductions and early treatment discontinuation owing to adverse events,” they said.
For instance, triple therapy had the highest incidence of both grade 3 and 4 infections (21.2%) and atrial fibrillation (7.8%).
The editorialists noted that there has been “a flurry of interest” in trials combining ibrutinib and venetoclax – as was done in the triple-therapy arm – since both emerged as powerful tools against CLL in recent years. However, even with the study results, they said “the use of triplet therapy should be viewed as investigational.”
For one thing, rates of uMRD were not “dramatically different” between triple therapy and venetoclax-obinutuzumab, and longer follow-up is better gauge differences in PFS and long-term toxicities.
Also, ibrutinib is being eclipsed by the second-generation Bruton’s tyrosine kinase inhibitors acalabrutinib and zanubrutinib, because they have better safety profiles, and they are being assessed in CLL combination trials. For now, there are too many unknowns for routine use of triple therapy in fit CLL patients, they said.
The investigators and editorialists both noted that improved uMRD in the study translated into superior PFS, raising the possibility that uMRD might be a valid alternative endpoint to PFS in CLL trials.
With “median remissions in CLL lasting far in excess of 5 years, designing studies that take 8-10 years” to reach a PFS endpoint is simply too slow. Moving to an alternative endpoint such a uMRD would preserve “the momentum that has been generated” with recent advances, Dr. Woyach and Dr. Byrd said.
The work was funded by the companies that market venetoclax, ibrutinib, and obinutuzumab: AbbVie, Janssen, and Roche. Dr. Eichhorst is a consultant and/or speaker for the companies and also reported grants from them. Dr. Byrd is a consultant/adviser for Eilean Therapeutics, Kurome Therapeutics, Newave, and Orbimed. Dr. Woyach disclosed ties with AbbVie, AstraZeneca, Lilly, and other companies.