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SAN DIEGO – Ibrutinib alone or in combination with rituximab resulted in superior progression-free survival (PFS) when compared with bendamustine plus rituximab in the randomized, phase 3 trial of older patients with previously untreated chronic lymphocytic leukemia (CLL).
“There was no difference in progression-free survival between ibrutinib and ibrutinib plus rituximab,” said Dr. Woyach of the Ohio State University, Columbus.
Median PFS in this study was 43 months in the BR arm, and was not reached in either of the ibrutinib-containing arms, she said. No significant differences in overall survival (OS) were seen among the treatment arms, which may have been because of short follow-up and the fact that patients in the BR arm were allowed to cross over to ibrutinib if they progressed on treatment.
Participants in the international, multicenter trial – a project of the National Cancer Institute National Clinical Trials Network – were 547 adults aged 65 years or older (median, 71 years) with previously untreated, symptomatic CLL. They were enrolled from 219 sites across the United States and Canada between Dec. 9, 2013, and May 16, 2016.
The three arms were well matched with respect to baseline characteristics except for a slightly higher number of patients with complex karyotypes in the IR arm, Dr. Woyach said.
Treatment in the BR arm included bendamustine 90 mg/m2 on days 1 and 2 of each 28-day cycle plus rituximab at a dose of 375 mg/m2 on day 0 of cycle 1 then 500 mg/m2 on day 1 of cycles 2-6. Patients in the ibrutinib arms received 420 mg daily until disease progression either with or without rituximab at 375 mg/m2 weekly for 4 weeks starting at cycle 2 day 1 and then given on day 1 of cycles 3-6.
Grade 3-5 treatment-emergent hematologic adverse events (AEs) occurred in 61%, 41%, and 38% of patients in the BR, ibrutinib, and IR arms, respectively. Neutropenia and thrombocytopenia occurred more often in the BR than in the ibrutinib arms. Nonhematologic AEs occurred in 63%, 74%, and 74%, respectively, with an overall greater incidence in the ibrutinib arms. Infections and sudden deaths were numerically but not significantly higher in the ibrutinib arms.
“We undertook this study to determine the most effective therapy for older patients with CLL,” Dr. Woyach said, explaining that while older patients make up the majority of patients with CLL, they are typically underrepresented in trials.
At the start of the study, BR was widely used and the Bruton’s tyrosine kinase inhibitor ibrutinib was “just entering the clinic,” she noted.
“Despite now-widespread use in the [front-line setting] following FDA approval for this indication in 2016, the efficacy of ibrutinib versus standard chemoimmunotherapy has not previously been investigated,” she said.
Since adding rituximab has been shown to improve PFS and OS when added to chemotherapy in CLL, she and her colleagues also looked at whether this was the case with ibrutinib as well.
“This is the only phase 3 trial designed to answer this question,” she noted, adding that the findings justify the use of ibrutinib as a standard-of-care treatment for CLL patients aged 65 years and older.
, of Dana-Farber Cancer Institute in Boston, who moderated the press briefing, agreed. “I think this really does indicate that ibrutinib as front-line therapy, which many clinicians have been doing, is a very reasonable practice.”
Dr. Woyach added, however, that while ibrutinib represents a major therapeutic advance, its cost and its toxicities in older patients are a concern that warrant close monitoring and development of strategies to reduce the need for long-term continuous treatment.
Additional phase 3 studies set to open soon will compare ibrutinib in combination with venetoclax and obinutuzumab with standard ibrutinib
Dr. Woyach reported having no disclosures. Dr. Steensma reported receiving research funding from, and/or serving as a consultant, board member, or adviser for Takeda Pharmaceutical, Syros Pharmaceuticals, Otsuka Pharmaceutical, Onconova Therapeutics, Novartis, Kura Oncology, Janssen, H3 Biosciences, Celgene, Amphivena Therapeutics, and Acceleron Pharma.
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