Descriptive Analysis of Dosing and Outcomes for Patients with Ibrutinib-Treated Relapsed or Refractory Chronic Lymphocytic Leukemia in a Canadian Centre

Background: Ibrutinib is an approved treatment for relapsed or refractory chronic lymphocytic leukemia (CLL) and small lymphocytic lymphoma (SLL). The effect of ibrutinib dose reduction compared with discontinuation in a population-based setting is unclear. Methods: To examine the patterns of ibrutinib use in a Canadian population-based setting, we analyzed a retrospective cohort of patients with relapsed or refractory CLL or SLL treated with ibrutinib. Results: The 64 patients diagnosed with cll or sll had a median age of 76.5 years. Most had unmutated ighv (immunoglobulin variable heavy chain). A hematologic response occurred in 39 patients regardless of the ibrutinib dose. The most common toxicities were infection, bruising or bleeding, and musculoskeletal problems, with a median time to first toxicity of 14 days. More than half the cohort experienced a dose reduction, with musculoskeletal problems, cytopenias, and infection being the leading causes; surgery was the most frequent indication for holding treatment. Only 26 of the 64 patients (40.6%) stayed on the recommended maximal dose of ibrutinib. No differences in reported toxicities or hematologic response rates were evident between the patients receiving maximal and submaximal therapy. At the end of the study period, 53 patients from the initial cohort remained on ibrutinib. Conclusions: More than half the study patients received ibrutinib therapy at a submaximal dose without evidence of increased frequency of toxicities or disease progression. The rate of ibrutinib discontinuation was lower in our cohort than has been reported in other settings. Submaximal ibrutinib dosing will have to be further systematically evaluated.