CHICAGO – The efficacy of ibrutinib is durable for patients with relapsed chronic lymphocytic leukemia (CLL), and combination strategies are showing the potential to improve on this benefit, based on results from three studies reported in a poster discussion session at the annual meeting of the American Society of Clinical Oncology.
Ibrutinib monotherapy
In the phase III randomized RESONATE trial, funded by Pharmacyclics, investigators compared ibrutinib with ofatumumab (Arzerra), an anti-CD20 antibody, among 391 patients with CLL or small lymphocytic lymphoma (SLL), with cross-over allowed. Initial results favored ibrutinib.
Investigators led by John C. Byrd, MD, director of the division of hematology at the Ohio State University Comprehensive Cancer Center in Columbus, reported updated data in a poster session at the meeting, now with a median 44 months of follow-up in the ibrutinib arm.
Median progression-free survival was not reached with ibrutinib, compared with 8.1 months with ofatumumab (hazard ratio, 0.133). The 3-year rate of progression-free survival was 59% and 3%, respectively.
The pattern was generally similar across patients stratified by cytogenetics (deletion of 17p, deletion of 11q, or neither), IGHV and TP53 mutation status, and prior lines of therapy, reported Dr. Byrd, who disclosed that he receives research funding from Pharmacyclics, among other companies.
The 3-year overall survival rate for ibrutinib was 74%. In analyses adjusted for cross-over, patients given the inhibitor had a markedly lower risk of death than did peers given the antibody (HR, 0.37).
The overall response rate with ibrutinib was 91%. Although the rate of complete response increased with follow-up, it was still just 9%.
The most common grade 3 or worse adverse events were neutropenia (23%), pneumonia (17%), and anemia, thrombocytopenia, and hypertension (8% each). Of patients, 6% each had a major hemorrhage and grade 3 or worse atrial fibrillation.
“These long-term results from the international phase III RESONATE study show that extended treatment with ibrutinib is tolerable and continues to show sustained PFS in previously treated patients with CLL regardless of high-risk cytogenetics,” the investigators conclude. “Traditional poor prognostic factors for survival with chemoimmunotherapy, including del(17p) and del(11q), were not significant factors predictive of [progression-free survival] outcomes with ibrutinib therapy.”
Dr. Jennifer R. Brown
Taken together, experience to date with ibrutinib highlights some issues and unmet needs, she said: greater treatment discontinuation in the real-world setting, early relapse in patients having higher-risk genetics or complex karyotypes, and an overall low rate of remission or minimal residual disease negativity.
These are important for several reasons, Dr. Brown maintained. “Persistent disease will lead to relapse eventually. If we have up to 40% discontinuation for adverse events, then, if people are in deeper remission at the time of discontinuation, they are likely to have a longer remission off drug. And, ultimately, of course, cure would require absence of disease,” she elaborated. “Then enhancing tolerability to keep patients on drug is an ongoing unmet need.”
Ibrutinib plus ublituximab and umbralisib
In a phase 1/1b trial funded by TG Therapeutics, investigators led by Loretta J. Nastoupil, MD, of the department of lymphoma/myeloma at the University of Texas MD Anderson Cancer Center, Houston, tested a triplet consisting of ibrutinib with ublituximab – another anti-CD20 antibody – and umbralisib (TGR-1202) – an oral PI3 kinase–delta inhibitor.
A total of 38 patients with generally heavily pretreated leukemias and lymphomas were studied, including 20 with CLL or SLL. Notably, eight patients (50%) with CLL had a 17p or 11q deletion.
The median time on study was 11.1 months, reported Dr. Nastoupil, who disclosed that she receives honoraria and research funding from TG Therapeutics and that she has relationships with other companies. The overall response rate for the 19 evaluable patients with CLL or SLL was 100% (complete response in 32%, partial response in 68%).
The main grade 3 or 4 adverse events in the entire trial population were neutropenia (18%) and pyrexia (8%). Only two patients discontinued treatment because of adverse events.
“An expansion cohort is ongoing at the highest dose, and we will clearly need more patients treated and longer follow-up to really know the efficacy,” commented Dr. Brown, the discussant for the poster session. “But overall, I think the safety looks encouraging with this combination.”
“Novel agent combinations are feasible and hold promise for deeper remission and/or time-limited therapy. Most of the excitement is focused around BTK and BCL-2 inhibitors, but there is clearly a role for kinase-kinase combinations because we see here that it was safe to combine ibrutinib with a PI3 kinase inhibitor,” she noted. “So, we should continue to pursue other kinase-kinase combinations, as well as BCL-2–kinase combinations.”
Ibrutinib plus CAR-T cells
In a pilot trial funded by Novartis, investigators led by Saar Gill, MD, PhD, of the hospital of the University of Pennsylvania in Philadelphia, tested the combination of ibrutinib with chimeric antigen receptor–T cells (CAR-T cells) against CD19, on the basis of preclinical evidence of synergy.
Trial participants were 10 patients with CLL or SLL who had not achieved complete response with ibrutinib. All had a 17p deletion or a p53 mutation, or a complex karyotype, and some had a known ibrutinib resistance mutation.
At 3 months, eight (89%) of nine evaluable patients had no evidence of disease in bone marrow, reported Dr. Gill, who disclosed that he receives research funding from Novartis (institutional) and has patents for CAR-T cells for acute myeloid leukemia, among other disclosures. Seven patients (78%) achieved a complete or partial radiographic response in the spleen and lymph nodes.
Overall, the treatment was well tolerated. One patient developed grade 4 tumor lysis syndrome, and two developed grade 3 cytokine release syndrome. But, none required anticytokine therapy.
Most patients remain on ibrutinib and are being monitored. In addition, the researchers plan to treat 25 more patients with the same combination.
“We don’t know what will happen if the patients stop ibrutinib at some point, which is a question for the future,” commented Dr. Brown, the discussant.
“CAR-T cell therapy in CLL has historically had lower response rates than in ALL, but preclinical and early clinical data support ongoing investigation of combination therapy with ibrutinib as it appears that ibrutinib may enhance the production and engraftment of the T cells,” she noted. “Ultimately, of course, the role of CAR-T cell therapy in CLL will require a very clear, well-defined safety [protocol] if it is being used in comparison to some of the oral drugs that we can maintain many of the patients on for a long time.”