NEW YORK, NY—The 4-year follow-up of the RESONATE trial suggests ibrutinib may provide long-term efficacy in previously treated patients with chronic lymphocytic leukemia (CLL).
The median progression-free survival (PFS) has not yet been reached in this trial, regardless of high-risk cytogenetics, according to Jennifer Brown, MD, PhD, of the Dana-Farber Cancer Institute in Boston, Massachusetts.
She presented the update at Lymphoma & Myeloma 2017. The follow-up study was awarded the best clinical CLL abstract of the meeting.
In the phase 3 RESONATE study, investigators compared ibrutinib—the first-in-class, once-daily, oral inhibitor of Bruton tyrosine kinase—to ofatumumab in previously treated CLL/small lymphocytic lymphoma (SLL).
The primary analysis showed ibrutinib significantly improved survival, with a 78% reduction in the risk of progression and a 57% reduction in the risk of death.
The phase 3 trial randomized 195 CLL/SLL patients to oral ibrutinib at 420 mg once daily and 196 patients to intravenous ofatumumab at an initial dose of 300 mg followed by 2000 mg for 11 doses over 24 weeks.
One hundred thirty-three patients progressed on ofatumumab and crossed over to receive once-daily ibrutinib.
In each arm, the median patient age was 67, more than half of patients had an ECOG status of 1, and more than half had advanced-stage disease.
High-risk genetic abnormalities were common, Dr Brown said, with deletion 11q in a third of patients in the ibrutinib arm and 31% in the ofatumumab arm. Another third in each arm had deletion 17p, while 51% in the ibrutinib arm and 46% in the ofatumumab arm had TP53 mutation.
About a quarter of the patients in each arm had complex karyotype, and 73% and 63% in the ibrutinib and ofatumumab arms, respectively, were IGHV-unmutated.
Ibrutinib significantly extended PFS compared with ofatumumab. At a median follow-up for ibrutinib of 44 months (range, 0.33 – 53), ibrutinib led to an 87% reduction in the risk of progression or death. The 3-year PFS rate was 59% with ibrutinib and 3% with ofatumumab.
Ibrutinib conferred a benefit in PFS across all baseline patient characteristics.
Among ibrutinib-treated patients, the 3-year PFS was 53% for patients with deletion 17p, 66% for those with deletion 11q but not deletion 17p, and 58% for those with neither abnormality.
Dr Brown noted how closely complex karyotype associates with high-risk cytogenetics. Forty-two percent of patients with 17p deletion had a complex karyotype, as did 23% of patients with 11q deletion and 15% of patients with neither 17p nor 11q deletion.
For IGHV-mutation status, Dr Brown said there is no difference in PFS with this degree of follow-up.
In terms of TP53 mutation status, Dr Brown pointed out a trend toward a worse PFS in those patients with the mutation.
“We actually looked by individual p53 mutation versus 17p deletion, versus both, versus neither, in the 2-year follow-up paper and found that p53 with 17p, both abnormalities, did have worse PFS than neither,” she said.
“This may require further follow-up because we do know that most 17p patients also have a p53 mutation, particularly in the relapsed setting.”
As expected, Dr Brown said, those patients with more than 2 prior therapies had a worse PFS compared to patients with 2 or fewer prior therapies.
Multivariate analysis demonstrated that more than 2 prior lines of therapy or an elevated ß2 microglobulin were associated with decreased PFS with ibrutinib.
When the investigators adjusted the overall survival data for cross-over, ibrutinib was projected to continue the overall survival benefit compared with ofatumumab, with a hazard ratio of 0.37.
Dr Brown noted that, early on, there’s quite a significant rate of partial response with lymphocytosis observed in patients on ibrutinib.
This “diminishes dramatically,” she said, but about 5% of patients at 3 and 4 years still have ongoing lymphocytosis.
“Similarly, initially, there’s a very low rate of complete remission, which has risen steadily to 9% at this follow-up,” she said.
And the overall response rate is 91%.
Treatment exposure and toxicity
The median duration of ibrutinib treatment is 41 months, and 46% of patients continue on treatment. Twenty-seven percent of patients discontinued due to progression, and 12% because of adverse events (AEs).
Of the 53 patients who discontinued therapy, 14 had transformation as their primary reason, 9 with diffuse large B-cell lymphoma, 3 with Hodgkin disease, and 2 with prolymphocytic lymphoma.
The most frequent AEs leading to discontinuation included pneumonia (n=3), anemia (n=2), thrombocytopenia (n=2), diarrhea (n=2), and anal incontinence (n=2).
AEs leading to discontinuation decreased over time—6% in year 0 to 1 and 4% in years 2 to 3.
“The most frequent cumulative AEs are similar to what we’ve seen in most prior studies,” Dr Brown said, including diarrhea, fatigue, and cough.
In terms of grade 3 or higher AEs, about a quarter of patients had neutropenia, 17% had pneumonia, and 8% had hypertension.
Six percent of patients had major hemorrhage, and all-grade atrial fibrillation occurred in 11% of patients.
“Now, many of the grade 3 and higher AEs did decline over time during the study,” Dr Brown noted. “You can see this is quite evident for neutropenia as well as pneumonia, and all infections declined from year 1 to subsequent years.”
Hypertension, in contrast, has been fairly steady over the later years, she said, and atrial fibrillation is highest in the first 6 months but then continues at a low rate thereafter.
The investigators believe these long-term results demonstrate that ibrutinib is tolerable and continues to show sustained efficacy in previously treated and high-genomic-risk patients with CLL. In addition, no long-term safety signals have emerged.
This study was sponsored by Pharmacyclics, LLC, an AbbVie company.