SAN DIEGO – The combination of ibrutinib and rituximab was associated with a two-thirds reduction in chronic lymphocytic leukemia (CLL) progression, compared with standard chemoimmunotherapy in patients younger than 70 years old, interim results of a phase 3 randomized trial showed.
Among 529 patients with previously untreated, symptomatic CLL randomly assigned to ibrutinib-rituximab (IR) or to chemoimmunotherapy with fludarabine, cyclophosphamide, and rituximab (FCR), the IR regimen was associated with a 65% reduction in risk for disease progression, which was the trial’s primary endpoint.
The IR regimen was also associated with better overall survival out to 4 years of follow-up, reported Tait D. Shanafelt, MD, of Stanford (Calif.) University.
“This establishes ibrutinib-based therapy as the most effective treatment tested to date in this disease for untreated patients,” he said at a media briefing prior at the annual meeting of the American Society of Hematology.
The study results are likely to dethrone FCR as the most active chemoimmunotherapy regimen against CLL, Dr. Shanafelt said.
In the ECOG-ACRIN Cancer Research Group E1912 trial, 529 patients aged 70 or younger with previously untreated CLL were enrolled and randomly assigned on a 2:1 basis to either standard therapy with six cycles of FCR according to standard protocols (175 patients), or IR, with ibrutinib 420 mg daily for each cycle, and rituximab delivered 50 mg/m2 intravenously on day 1 of cycle 2, and 325 mg/m2 on day 2 of the same cycle, and 500 mg/m2 on day 1 for all remaining cycles (354 patients).
From cycle 8 until progression, patients in the IR arm received daily ibrutinib 420 mg.
Dr. Shanafelt presented results from both an intention-to-treat analysis and a per-protocol analysis excluding 22 patients in the IR arm and 9 patients in the FCR arm who were randomized but later found not to meet eligibility criteria.
After a mean follow-up of 34 months, there were 37 PFS events in the IR arm, compared with 40 events in the FCR arm in an intention-to-treat analysis. The difference translated into a hazard ratio for progression of 0.35 with IR (P less than .00001).
The results were similar in the per-protocol analysis, with an HR of 0.32 favoring IR (P less than .00001).*
There were four deaths in the IR arm, compared with 10 in the FCR arm at the time of the data lock, translating into a hazard ratio (HR) for overall survival of 0.17 (P less than .0003) in the intention-to-treat analysis, and 0.13 in the per-protocol analysis (P less than .0001).
Dr. Shanafelt noted that although the overall number of deaths was relatively small, there were twice as many patients enrolled in the IR arm as in the FCR arm, meaning that the rate of deaths in the FCR arm was fivefold higher than in the IR arm.
In a subgroup analysis of PFS, IR was superior to FCR regardless of patient age, sex, performance status, disease stage, or the presence or absence of the 11q23.3 deletion.
PFS was also significantly better with IR in patients with unmutated immunoglobulin heavy chain variable (IGHV) regions (HR 0.26, P less than .00001), but not in patients with mutated IGHV.*
Grade 3 or greater treatment-related adverse events occurred in 58.5% of patients in the IR arm, compared with 72.1% of patients in the FCR arm. Specific events that occurred significantly less often with IR included neutropenia (22.7% vs. 43.7%), anemia (2.6% vs. 12.0%), thrombocytopenia (2.9% vs. 13.9%), any infection (7.1% vs. 19.0%), and neutropenic fever (2.3% vs. 15.8%; P less than .001 for all comparisons).
Events that occurred more frequently with IR than FCR included atrial fibrillation (2.9% vs. 0%, P = .04), and hypertension (7.4% vs. 1.9%, P = .01).
Dr. Shanafelt acknowledged that one possible barrier to the IR regimen is cost; the monthly cost of ibrutinib maintenance is about $10,000, he said, although he noted that cost considerations were not studied in the trial.
“Future trials testing novel agent combinations to see if we can eliminate the need for chronic therapy should be pursued,” he said.
The trial was sponsored by the National Cancer Institute with additional support from Pharmacyclics. Dr. Shanafelt reported patents and royalties from the Mayo Clinic, and research funding from Celgene, GlaxoSmithKline, Genentech, Abbvie, Pharmacyclics, and Janssen.
SOURCE: Shanafelt TD et al. ASH 2018, Abstract LBA-4.
*Correction, 12/12/2018: An earlier version of this story misstated the P value in two comparisons.