Ibrutinib, an orally administered covalent inhibitor of Bruton tyrosine kinase (BTK), is an effective therapy for patients with relapsed chronic lymphocytic leukemia (CLL). We investigated the activity and safety of the combination of ibrutinib with the monoclonal antibody rituximab (iR) in patients with high-risk CLL.
In this single-arm, phase 2 studywe enrolled 40 patients with high-risk CLL at MD Anderson Cancer Center, Houston, Texas, USA. Patients with symptomatic CLL requiring therapy received 28 day cycles of once-daily ibrutinib 420 mg , together with rituximab (weekly during cycle 1, then once per cycle until cycle 6), followed by continuous single-agent ibrutinib. The primary endpoint was progression-free survival (PFS) in the intention-to-treat population. This study is registered with ClinicalTrials.gov, number NCT01520519 and is no longer accruing patients.
Between February 28, 2012 and September 11, 2012, we enrolled 40 CLL patients with high-risk disease features. 20 patients had del17p or TP53 mutations (16 previously treated, 4 untreated), 13 had relapsed CLL with del11q, and 7 patients a PFS < 36 months after frontline chemo-immunotherapy. Toxicity was mainly of mild to moderate severity (grade 1–2). 10 (25%) patients had diarrhea (grade 1 in 9 [22.5%] patients, grade 2 in 1 [2.5%]), bleeding events occurred in 14 (35%) patients (8 [20%] patients with grade 1, 5 [12.5%] patients grade 2, and 1 [2.5%] grade 3), nausea in 15 (37.5) patients (10 [25%] grade 1, 5 [12.5%] grade 2), and fatigue in 7 (17.5%) patients (4 [10%] grade 1, 3 [7.5%] grade 2). Grade 3 infections occurred in 4 patients (10%), no grade 4 or 5 infections occurred. At 18 months, the Kaplan Meier estimate of progression-free survival was 78% (95% CI 60.6–88.5) (del[17p] or TP53 mutation: 72%, 95% CI: 45.6–87.6)
Ibrutinib in combination with rituximab is a well-tolerated regimen for patients with high-risk CLL. It induces high rates of remissions and has positive impact on QOL in this difficult-to-treat patient population. These encouraging data merit further investigation of the added benefit of rituximab as combination partner for ibrutinib in an ongoing randomized trial, in which single-agent ibrutinib is compared to iR combination therapy (NCT02007044).
Pharmacyclics, Inc., Cancer Prevention and Research Institute of Texas (CPRIT), Leukemia & Lymphoma Society, NCI Grant P30 CA016672, MD Anderson’s Moon Shot Program in CLL, and MD Anderson Cancer Center Support Grant CA016672.