A combination of venetoclax and ibrutinib may be a safe and effective treatment option for previously untreated elderly and high-risk patients with chronic lymphocytic leukemia (CLL), according to investigators of a phase 2 trial of the combination.
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About 88% of patients achieved complete remission or complete remission with incomplete count recovery after 12 cycles of treatment, reported lead author Nitin Jain, MD, of the University of Texas MD Anderson Cancer Center, Houston, and colleagues.
There were no new safety signals for the combination of ibrutinib, an irreversible inhibitor of Bruton’s tyrosine kinase, and venetoclax, a B-cell lymphoma 2 protein inhibitor, the investigators noted.
“This combination was reported to be safe and active in patients with mantle cell lymphoma,” they wrote in the New England Journal of Medicine. “Given the clinically complementary activity, preclinical synergism, and nonoverlapping toxic effects, we examined the safety and efficacy of combined ibrutinib and venetoclax treatment in previously untreated patients with CLL.”
In particular, the investigators recruited older patients, as this is a common population that can be challenging to treat. “Because CLL typically occurs in older adults, the majority of patients who need treatment are older than 65 years of age,” the investigators wrote. “This group of patients often has unacceptable side effects and has a lower rate of complete remission and undetectable minimal residual disease with chemoimmunotherapy than younger patients.”
The open-label, phase 2 trial enrolled 80 elderly and high-risk patients with previously untreated CLL. Eligibility required an age of at least 65 years or presence of at least one high-risk genetic feature; namely, mutated TP53, unmutated IgVH, or chromosome 11q deletion.
In order to reduce the risk of tumor lysis syndrome, ibrutinib (420 mg once daily) was given as monotherapy for three 28-day cycles. From the fourth cycle onward, venetoclax was also given, with weekly dose escalations to a target dose of 400 mg once daily. The combination was given for 24 cycles, with treatment continuation offered to patients who were still positive for minimal residual disease.
The median patient age was 65 years, with 30% of the population aged 70 years or older. A large majority (92%) had at least one high-risk genetic feature.
Following initiation with three cycles of ibrutinib, most patients had partial responses, the investigators wrote; however, with the addition of venetoclax, responses improved over time. Of all 80 patients, 59 (74%) had a best response of complete remission or complete remission with incomplete count recovery.
After six cycles, 51 out of 70 patients (73%) achieved this marker. After 12 cycles, 29 of 33 patients (88%) had this response, with 61% of the same group demonstrating undetectable minimal residual disease in bone marrow.
After 18 cycles, 25 of 26 patients (96%) had complete remission or complete remission with incomplete count recovery, 18 of which (69%) were negative for minimal residual disease. Three patients completed 24 cycles of combined therapy, all of whom achieved complete remission or complete remission with incomplete count recovery and undetectable minimal residual disease.
Focusing on patients aged 65 years or older, 74% had complete remission or complete remission with incomplete count recovery after six cycles of therapy and nearly half (44%) had undetectable minimal residual disease. After 12 cycles, these rates increased to 94% and 76%, respectively. Responses were also seen across genetically high-risk subgroups.
One patient died from a cryptococcal infection of the central nervous system; this was deemed unrelated to treatment, as symptoms began prior to initiation of treatment and only one dose of ibrutinib was given.
The estimated 1-year progression-free survival rate was 98% and the estimated overall survival rate was 99%. At the time of publication, no patients had disease progression.
Among all patients, 60% experienced grade 3 or higher adverse events, the most common being neutropenia (48%).
Almost half of the patient population (44%) required dose reductions of ibrutinib, most commonly because of atrial fibrillation, and 24% required dose reductions of venetoclax, most often because of neutropenia.
“Our data showed that combination therapy with ibrutinib and venetoclax was effective in patients with CLL, with no new toxic effects from the combination that were not reported previously for the individual agents,” the investigators wrote, adding that the efficacy findings were also “substantially better” than what has been reported with monotherapy for each of the agents in patients with CLL.
The study was funded by AbbVie, the University of Texas MD Anderson Cancer Center Chronic Lymphocytic Leukemia Moon Shot program, the Andrew Sabin Family Foundation, and the CLL Global Research Foundation. The investigators reported relationships with AbbVie, Incyte, Celgene, and other companies.
SOURCE: Jain N et al. N Engl J Med. 2019;380:2095-103.