Three studies presented at the ongoing 59th Annual Meeting and Exposition of the American Society of Hematology in Atlanta, Georgia, shared progress on the oral Bruton’s tyrosine kinase inhibitor, ibrutinib, in the treatment of relapsed/refractory mantle cell lymphoma (MCL) and as a single agent in chronic lymphocytic leukemia (CLL).
Three studies presented at the ongoing 59th Annual Meeting and Exposition of the American Society of Hematology (ASH), Atlanta, Georgia, shared progress on the oral Bruton’s tyrosine kinase inhibitor, ibrutinib, in the treatment of relapsed/refractory mantle cell lymphoma (MCL) and as a single agent in chronic lymphocytic leukemia (CLL).
The MCL results were a 3.5-year follow-up of a pooled analysis of 370 patients with relapsed/refractory MCL who were treated with ibrutinib as part of 3 open-label studies: SPARK, RAY, and PCYC-1104. This longer-term follow-up, which included additional exposure to treatment, was conducted in 87 patients across the 3 studies who enrolled in the long-term access study CAN3001—a phase 3b open-label study.1
Patients received 560 mg ibrutinib orally, once daily, until progressive disease or unacceptable toxicity. Patients in the SPARK study were required to have received both rituximab and bortezomib, while those in the RAY study required prior treatment with rituximab. Only those patients who continued to benefit from ibrutinib therapy at end of the study could enroll in CAN3001. Crossover patients were excluded from the final pooled analysis. The study evaluated investigator-assessed tumor response, progression-free survival (PFS), and overall survival (OS). The median duration of follow-up in the pooled data set was 41.1 months (95% CI, 37.3-42.5); median treatment exposure was 11.1 months (range, 0.03-72.1). Fifty-four of the 87 (62.1%) patients enrolled in CAN3001 remain on ibrutinib, and had received at least 2 prior lines of treatment (LOT)
At 41-months follow-up, 26.5% patients achieved complete response (CR). Median PFS was 13.0 months in the overall patient population; in patients with 1 prior LOT, PFS was 33.6 months (range, 19.4-42.1) and in patients achieving CR, PFS was 46.2 months (range, 42.1-not estimable). Median OS was 26.7 months:
Grade 3 or greater treatment-related adverse events occurred in 295 (79.7%) patients, with the new onset events decreasing after the first year, the authors reported. The most common grade ≥ 3 TEAEs were neutropenia (17.0%), thrombocytopenia (12.2%), pneumonia (11.9%), anemia (9.5%), atrial fibrillation (5.9%), and hypertension (5.1%)—a majority were more common during the first year of ibrutinib treatment. Treatment-emergent severe adverse events (SAEs) occurred in 229 (61.9%) patients and new-onset SAEs decreased over time.
Another presentation at the meeting reported results from a crossover study that compared single-agent ibrutinib (RESONATE-2) and chemoimmunotherapy regimens in treatment-naïve patients with CLL from published studies with the following regimens:2
Limitations of the current analysis, the authors write, were the lack of available patient-level data from the chemoimmunotherapy studies and differences in study design and patient eligibility criteria.
The median age across the studies was 61—74 years; older patients usually enrolled in studies with ibrutinib, G-Clb, or R-Clb. Median CIRS scores ranged from 1–9, with lower comorbidity scores for patients treated with BR, FCR-CLL10, and FCR-CLL8.
Treatment with single-agent ibrutinib, the authors report, was associated with longer PFS compared with chemoimmunotherapy regimens; particularly, PFS with ibrutinib compared favorably to chemoimmunotherapy studies that also excluded patients with del(17p) (BR and FCR-CLL10), and those that enrolled older patients with comorbidities (G-Clb, R-Clb, and Ofa-Clb). In patients with unmutated IGHV, PFS HR, compared with chlorambucil, was 0.08 (95% CI, 0.04-0.17) for ibrutinib, 0.23 (95% CI, 0.16-0.34) for G-Clb, and 0.54 (95% CI, 0.38-0.76) for R-Clb. In patients with del(11q), PFS HR compared with chlorambucil, was 0.02 (95% CI, 0.005-0.11), 0.37 (95% CI, 0.17-0.81) and 0.99 (0.49-2.03) for ibr, G-Clb, and R-Clb, respectively.
PFS rates across baseline groups were favorable with ibrutinib, compared with BR or FCR regimens in CLL10, especially in patients who had advanced disease, bulky lymph nodes, unmutated IGHV, and del(11q).
OS with single-agent ibrutinib favored chemoimmunotherapy in studies with older or less fit patients; however, compared with chlorambucil, OS with ibrutinib alone was better relative to Ofa-Clb, R-Clb, and G-Clb.
The overall rate of grade ≥3 adverse events for chemoimmunotherapy regimens was highest with FCR, followed by BR and chlorambucil-based regimens; the rate was similar for ibrutinib and G-Clb despite the longer data collection period for ibrutinib. The rate of grade ≥3 infections varied by study and ranged from 9% with Ofa-Clb to 40% with FCR-CLL10, and was 25% with ibrutinib. Rates of grade ≥3 cytopenias were generally lower with ibrutinib compared with chemoimmunotherapy.
Despite its limitations, the authors propose that their cross-trial comparison suggests that ibrutinib may potentially eliminate the need for chemotherapy in some patients with treatment-naive CLL.
Quality-of-life observations from the phase 3 RESONATE-2 study—conducted in older, treatment-naïve patients with CLL or small lymphocytic leukemia—were also presented at the ASH meeting.7 With respect to clinical outcomes, single-agent ibrutinib in this patient population reduced the risk of disease progression or death by 84%, compared with chlorambucil, at a median follow-up of 18.4 months.
Patients (65 years or older) were randomized to receive 420 mg ibrutinib once daily until progressive disease, or chlorambucil for up to 12 months. Patients who progressed on chlorambucil had the option of receiving second-line ibrutinib. The various patient-reported outcomes (PROs) that were measured included: FACIT-Fatigue, EQ-5D-5L, Q-TWiST, and EORTC QLQ-C30 global health status.
The median follow-up among 269 patients, who had initiated therapy due to progressive marrow failure (38%), lymphadenopathy (37%), splenomegaly (30%), fatigue (27%), or night sweats (25%), was 35.7 months with ibrutinib and 34.4 months with chlorambucil. Ibrutinib treatment resulted in significantly longer PFS compared with chlorambucil (median, not reached vs 15.0 months); additionally, there was an 87% reduction in risk of progression or death with ibrutinib (HR, 0.130; 95% CI, 0.081, 0.208).
Importantly, for this particular study, the authors report greater and sustained improvements in PROs, which improved over time:
Based on their Q-TWiST analysis at a median follow-up of 18.4 months, the authors report that the mean time spent without symptoms of disease progression or grade 3-4 treatment toxicity was longer with ibrutinib (501 vs 351 days; 95% CI, 109, 193).