“This trial led to the first-line approval of ibrutinib for CLL patients,” lead author Paul M. Barr, MD, of the University of Rochester (N.Y.), said in an interview. “It is important to follow these patients long-term to understand the expected duration of response/disease control and to monitor for late toxicity,” he said “The data are useful in guiding clinicians who treat CLL and patients being treated with single agent BTK inhibitors,” he noted.
In the initial RESONATE-2, a phase 3, open-label study, 269 adults aged 65 years and older who were previously untreated for CLL or small lymphocytic leukemia were randomized to ibrutinib or the standard of care, chlorambucil. Patients received 420 mg of ibrutinib once daily until disease progression or unacceptable toxicity (136 patients) or up to 12 cycles of 0.5-0.8 mg/kg of chlorambucil (133 patients).
The long-term outcome data were published in Blood Advances
Overall, at a median of 83 months’ follow-up, progression-free survival was significantly higher for ibrutinib patients than for chlorambucil patients (hazard ratio 0.154).
At 7 years, progression-free survival was 59% in the ibrutinib group vs. 9% in the chlorambucil group.
Notably, progression-free survival benefits with ibrutinib also were higher for patients with high-risk genomic features, identified as del(11q) and unmutated immunoglobulin heavy-chain variable region gene (IGHV).
Complete data were available for 54 patients with del(11q) and 118 with unmutated IGHV. In this subset of patients, progression-free survival rates at 7 years were significantly higher for those treated with ibrutinib vs. chlorambucil who had del(11q) or unmutated IGHV (52% vs. 0% and 58% vs. 2%, respectively).
Approximately 42% of patients with chronic lymphocytic leukemia treated with ibrutinib remained on the therapy at up to 8 years, with a median follow-up of 7.4 years. Overall survival at 7 years was 78% for ibrutinib; overall survival data were not collected for chlorambucil for patients with progressive disease after the median of 5 years, as these patients were eligible to switch to ibrutinib in a long-term extension study or exit the study.
Adverse events prompted reduction of ibrutinib in 30 patients and dose holding for at least 7 days in 79 patients. However, dose modification resolved or improved the adverse events in 85% of the patients with held doses and 90% of those with reduced doses.
The overall prevalence of adverse events was similar to previous follow-up data at 5 years. No new safety signals were observed during the longer study period. The rate of treatment discontinuation because of adverse events was highest in the first year.
“We have been surprised at how long the remissions have lasted with ibrutinib,” said Dr. Barr. “Even with up to 8 years of follow-up, we have yet to reach the median progression free-survival,” he noted.
“These data, in combination with other data sets, highlight the impact that ibrutinib and other BTK inhibitors have had in treating CLL,” said Dr. Barr. “Patients are living longer and avoiding the side effects of chemotherapy in the era of novel agent use,” he said.
However, research gaps remain, Dr. Barr noted. “We need to continue following these patients over time given the length of the remissions. Additionally, we need to continue investigating novel combinations,” he said. Such studies will help us understand the benefit of fixed durations regimens compared to single agent BTK inhibitors,” he emphasized.