Prolonged exposure to ibrutinib showed sustained progression-free and overall survival and had tolerable safety outcomes in patients with relapsed or refractory chronic lymphocytic leukemia, according to a post hoc analysis of the phase 3 RESONATE trial.
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“This study ... provides further evidence for efficacy and safety with prolonged treatment across multiple high-risk genomic and clinical disease features and with increasing depth of response,” John C. Byrd, MD, of the Ohio State University, Columbus, and his colleagues wrote in Blood.
RESONATE included 391 high-risk patients with relapsed or refractory chronic lymphocytic leukemia (CLL). Study participants were randomized in a 1:1 fashion to receive ibrutinib 420 mg daily or ofatumumab (initial infusion of 300 mg followed by seven weekly infusions and four monthly infusions of 2,000 mg) for a maximum of 24 weeks. Drug therapy was continued until cancer progression or intolerable toxicity of either agent was seen.
“Primary analysis at median follow-up of 9.7 months demonstrated superiority of ibrutinib over ofatumumab in PFS [progression-free survival], OS [overall survival], and overall response,” the researchers wrote. “With extended follow-up of median 44 months, these same results persist; a plateau of PFS has not yet been reached in this long-term follow-up. We also observe very durable remissions among patients of all genomic groups, including those with del(17)(p13.1), del(11)(q22.3), or unmutated IgHV [immunoglobulin heavy chain gene], who are traditionally considered high-risk populations.”
After an extended follow-up (median, 44 months), the team found that the PFS benefit with ibrutinib was sustained, compared with ofatumumab (hazard ratio, 0.133; 95% confidence interval, 0.099-0.178; P less than .0001). The 3-year PFS rate was 59% for ibrutinib, compared with 3% for ofatumumab. Similar PFS benefits were seen among subgroups of high- and very high–risk patients, based on their scores on the International Prognostic Index for CLL.
The OS benefit was also sustained in those randomized to ibrutinib (HR, 0.591; 95% CI, 0.378-0.926; P = .0208). The continued OS benefit with ibrutinib versus ofatumumab continued even after a sensitivity analysis adjusted for crossover of patients to ibrutinib.
With respect to safety, adverse events of any grade were similar to previous reports of ibrutinib. In fact, the prevalence of adverse events (grade 3 or higher) decreased over time for participants that continued on ibrutinib.
“Multiple studies are ongoing to investigate ibrutinib earlier in the course of CLL therapy, including phase 3 studies of first-line ibrutinib [or ibrutinib combined with anti-CD20 therapy], compared with standard chemoimmunotherapy regimens,” they wrote.
The study was sponsored by Pharmacyclics and Janssen. The authors reported financial disclosures related to the sponsors and several other companies.
SOURCE: Byrd JC et al. Blood. 2019 Mar 6. doi: 10.1182/blood-2018-08-870238.