Initial results from the trial were shown at the EHA 2019 annual meeting and reported at the time by this news organization.
They revealed that, among more than 430 CLL patients with a median age of over 70 years and multiple comorbidities, the combination of venetoclax, a B-cell lymphoma 2 protein blocker, plus obinutuzumab, an anti-CD20 monoclonal antibody, was associated with a 65% improvement in PFS, compared with chlorambucil, a chemotherapy agent, plus obinutuzumab.
On the strength of these findings, the venetoclax-obinutuzumab combination received Food and Drug Administration approval for previously untreated CLL and small lymphocytic lymphoma in March 2019.
The latest analysis, presented by Othman Al-Sawaf, MD, University Hospital of Cologne (Germany), showed that despite having just 12 cycles of treatment, patients treated with venetoclax-obinutuzumab continued to experience a significant PFS benefit over those given the chemotherapy-based regimen, including in high-risk patients, after more than 6 years of follow-up.
Dr. Al-Sawaf noted that more than 50% of patients given the experimental combination remained without a PFS event at the latest follow-up, and that over 60% had not required a second treatment, equating to a 66% reduction in the likelihood of needing a second treatment versus chlorambucil-obinutuzumab.
Dr. Al-Sawaf said at a press conference that, “clinically, the standard of care for any CLL if it is asymptomatic” is watch and wait, which is “true in the frontline setting, but also in the relapse setting.”
Therefore, these patients “do not need to initiate the next line of treatment, and that’s why time to next treatment is so interesting.”
He added that there also were no new safety signals, with adverse event rates dropping markedly once treatment was over, although there was a suggestion of an increase in second malignancies with venetoclax-obinutuzumab.
“We’ve seen, in many studies now that use fixed-duration approaches, that there is virtually no posttreatment toxicity once patients are able to get off treatment,” Dr. Al-Sawaf said, adding: “This really highlights the benefit” of stopping treatment, “which is a clear advantage compared to having any kind of continuous treatment.”
Approached for comment, William G. Wierda, MD, PhD, professor, department of leukemia, division of cancer medicine, University of Texas MD Anderson Cancer Center, Houston, emphasized the value of the 6-year follow-up of the study, adding that these are “very impressive data.”
He told this news organization that, in terms of the ongoing PFS improvement, “we wouldn’t expect anything otherwise” with venetoclax-obinutuzumab when compared with the chemotherapy-based regimen, but that the trend for an improvement in overall survival is of particular interest.
This “is a notable feature of the update,” Dr. Wierda said, and “we will continue to watch the long-term overall survival curves with a longer follow-up,” especially as the separation of the curves between the two regimens is “more prominent” than in previous analyses of CLL14.
He also pointed to the low incidence of grade ≥ 3 adverse events in patients who are in remission, which “support the use of fixed-duration chemo-free” treatments, and the longer follow-up now allowing the contribution of high-risk features to outcomes to be teased out in multivariate analysis.
“The data that we’re looking for in the next update of this is some indication about improved outcomes between patients with a mutated and unmutated immunoglobulin heavy chain gene [IgHV], in regard to undetectable MRD [minimal residual disease] status,” Dr. Wierda said.
“We know that mutational status correlates with progression free survival,” he explained. “What we would like to see moving forward is how that is associated with undetectable MRD status at the end of treatment.”
Dr. Wierda said that the next hotly anticipated trial in the field is CLL17, which is comparing ibrutinib monotherapy to fixed-duration venetoclax-obinutuzumab to fixed-duration ibrutinib-venetoclax in patients with previously untreated CLL.
“That’s the next question: Is there any advantage of a BTK [Bruton’s tyrosine kinase] inhibitor with venetoclax over venetoclax plus the CD20 antibody?”
Dr. Al-Sawaf, in presenting the latest analysis, reminded the audience that CLL14 was a randomized phase 3 study focusing on patients with previously untreated CLL and coexisting conditions who were randomized to either venetoclax-obinutuzumab for six cycles, followed by six cycles of venetoclax, or chlorambucil-obinutuzumab for six cycles, followed by chlorambucil for six cycles.
The patients, who were enrolled between 2015 and 2016, were required to have a Cumulative Illness Rating Scale (CIRS) score > 6 and/or creatinine clearance < 70 mL/min, which Dr. Al-Sawaf explained serves as “indicator of the unfitness of the patients.”
A total of 432 patients took part in the study. The median age across the two treatment groups was 71-72 years, and the median total CIRS score was 8-9. The majority of patients (79%-80%) had Binet stage B or C CLL. An intermediate tumor lysis syndrome risk was identified in 64%-68%.
“We also had a fair share of patients with high-risk disease,” Dr. Al-Sawaf noted, with approximately 60% having an unmutated IGHV status, and 12% having a TP53 mutation, both of which are associated with a poorer prognosis.
He added that the “aim of these long-term observations that we try to do every year is not so much to do the comparisons to chlorambucil-obinutuzumab, which we appreciate is not necessarily a standard of care anymore,” but rather to understand the safety and effectiveness of venetoclax-obinutuzumab “in the long run, given that all patients are off treatment.”
Beginning with the safety data, Dr. Al-Sawaf showed that rates of grade ≥ 3 adverse events plummeted after the treatment period, with rates of neutropenia falling from 51.9% with venetoclax-obinutuzumab and 47.2% with chlorambucil-obinutuzumab during treatment to 3.8% and 1.9%, respectively, post treatment.
Similarly, rates of thrombocytopenia decreased from 14.2% on treatment to 0.5% off treatment in patients given venetoclax-obinutuzumab, and from 15.0% to 0.0% in the chlorambucil-obinutuzumab group.
One note of caution was sounded over the proportion of patients with at least one second primary malignancy following treatment, which was numerically higher with venetoclax-obinutuzumab, at 14.2% versus 8.4% with the chemotherapy-based regimen.
“But this is a rather a heterogeneous pattern of solid organ tumors and melanoma,” Dr. Al-Sawaf said, referring to the additional malignancies in the venetoclax-obinutuzumab arm. These included lung cancer, prostate cancer and breast cancer.
He said, however, there was no “specific pattern that we can really pinpoint ... and, importantly, the difference is not statistically significant.”
Turning to the efficacy outcomes, Dr. Al-Sawaf showed that, after median follow-up of 76.4 months, the separation in PFS between the two treatment arms continued, with the median PFS 76.2 months with venetoclax-obinutuzumab versus 36.4 months with chlorambucil-obinutuzumab, at a hazard ratio 0.40 (P < .0001).
The 6-year PFS rate in patients treated with venetoclax-obinutuzumab was 53.1% versus 21.7% with the chemotherapy-based regimen. Looking at the high-risk groups, Dr. Al-Sawaf reported that there was a similar pattern of benefit with venetoclax-obinutuzumab.
Among patients with a TP53 mutation, the median PFS was 51.9 months with the combination versus 20.8 months in those given chlorambucil-obinutuzumab, while the corresponding durations in patients with unmutated IGHV were 64.8 months and 26.9 months, respectively.
Multivariate analysis demonstrated that IGHV status was an independent predictor of PFS in patients treated with venetoclax-obinutuzumab, as was the presence of a TP53 mutation, and lymph node size ≥ 5 cm.
There was no significant difference in overall survival between the two treatment groups, although there was a numerical difference in 6-year overall survival rates, at 78.7% with the experimental combination versus 69.2% with chlorambucil-obinutuzumab.