ORLANDO – Monotherapy with ibrutinib (Imbruvica) prolonged survival longer than did standard chemotherapy using chlorambucil (Leukeran) in the front-line treatment of older patients with chronic lymphocytic leukemia (CLL) or small lymphocytic lymphoma (SLL) in the phase III RESONATE-2 study.
Co–drug developers Pharmacyclics and Janssen Biotech announced this summer that ibrutinib, an orally bioavailable, small-molecule inhibitor of Bruton’s tyrosine kinase, had achieved its primary and secondary endpoints.
Courtesy: Neil Osterweil
Dr. Alessandra Tedeschi
But the first full look at the data at the annual meeting of the American Society of Hematology showed ibrutinib reduced the risk of progression or death by 84% by independent review compared with chlorambucil, which has been a standard first-line therapy in older CLL patients.
The results were simultaneously published in the New England Journal of Medicine (doi: 10.1056/NEJMoa1509388).
With a median follow-up of 18.4 months, median progression-free survival (PFS) had not been reached with ibrutinib vs. 19 months with chlorambucil (hazard ratio, 0.16; P less than .001).
By investigator assessment, ibrutinib reduced the risk of progression by 91%, with an 18-month PFS rate of 94% vs. 45% with chlorambucil (HR, 0.09; P less than .001).
The PFS benefit with ibrutinib was consistent regardless of patient age, Rai stage, ECOG (Eastern Cooperative Oncology Group) status, bulky disease, and importantly, such high-risk markers as chromosome 11q deletion and unmutated immunoglobulin heavy chain variable (IGHV) mutation status, study author Dr. Alessandra Tedeschi, of Hospital Niguarda Cà Granda, Milan, , said at a press briefing highlighting the study (Ab. 485).
In addition, ibrutinib led to an 84% reduction in the risk of death compared with chlorambucil (HR, 0.16; P = .001). The 24-month overall survival rate was 98% with ibrutinib versus 85% with chlorambucil.
Single-agent ibrutinib was approved in 2014 for patients with CLL who had received at least one prior therapy and for all patients with the deleterious 17p deletion on the basis of the phase III RESONATE trial in relapsed or refractory CLL.
Three-year follow-up in the phase II PCYC-1102 study signaled a benefit with ibrutinib in treatment-naive CLL, showing an overall response rate of 84%, 30-month PFS of 96%, and overall survival rate of 97% in a subset of 31 patients at least 65 years old (Blood. 2015 Apr 16;125[16]:2497-506).
“The phase III RESONATE-2 trial confirms the efficacy of ibrutinib in treatment-naive CLL patients, leading to a 91% reduction in risk of progression and 84% reduction in risk of death when compared to chlorambucil,” Dr. Tedeschi said.
In all, 269 patients, median age of 73 years, were evenly randomized to once-daily ibrutinib 420 mg until progression or unacceptable toxicity or chlorambucil 0.5 mg/kg (up to a maximum of 0.8 mg/kg) on days 1 and 15 of a 28-day cycle for up to 12 cycles. Patients with the deleterious 17p deletion were excluded, as single-agent chlorambucil is not effective in this population.
Ibrutinib significantly improved bone marrow function, as reflected by a sustained increase in hemoglobin and platelets.
“This is very important in this category of elderly patients, in whom bone marrow failure is the most common cause of morbidity,” Dr. Tedeschi said.
There were 3 deaths on the ibrutinib arm and 17 on the chlorambucil arm.
The majority of patients (87%) in this older population with frequent comorbidities was able to continue on oral, once-daily ibrutinib with a median of 1.5 years of follow-up, she said.
The most common adverse events on ibrutinib were grade one diarrhea, fatigue, cough, and nausea that did not result in treatment discontinuation. On the chlorambucil arm, fatigue nausea, vomiting, and cytopenias occurred more frequently than with ibrutinib.
Grade 3 maculopapular rash occurred in 3% with ibrutinib and 2% with chlorambucil, she said.
Ibrutinib was associated with higher and not insignificant rates of atrial fibrillation and major hemorrhage compared with chlorambucil, said Dr. Brian T. Hill of the Taussig Cancer Institute at the Cleveland Clinic, who was not involved in the study. In our interview, Dr. Hill also questions the relevance today of chlorambucil monotherapy as the comparator arm in RESONATE-2.
Pharmacyclics, which is jointly developing ibrutinib with Janssen Biotech, sponsored the study. Dr. Tedeschi reported having nothing to disclose. Several coauthors reported relationships with Pharmacyclics and Janssen.