Treatment Interruption and Regimen Change in Firstgeneration versus Second-generation Tyrosine Kinase Inhibitors used as First-line Therapy for Chronic Myeloid Leukemia

Background: Research has shown that treatment interruptions are associated with worse failure-free survival in chronic myeloid leukemia (CML); however they are commonly used in clinical trials to manage adverse events. Objectives: This study assessed the comparative rates of treatment interruption and regimen change between patients initiating first-line therapy with a first-generation tyrosine kinase inhibitor (1GTKI) imatinib versus second-generation TKI (2GTKI), dasatinib or nilotinib, for the treatment of CML in clinical practice. Methods: This was a retrospective cohort study using the Humana Research Database. Patients with CML who were between the ages of 18 and 89 and newly initiated 1GTKI or 2GTKI therapy between June 1, 2010 and December 31, 2011 were included. Treatment interruption and regimen change were compared using multivariable Cox proportional hazard regression models. Treatment interruption was defined as a gap in any TKI pharmacy claim that was longer than an allowable refill gap plus days’ supply from the previous TKI medication claim. Regimen change was defined as 1) a prescription claim for a different TKI therapy, or 2) increase in dose for the same medication. Results: 368 patients met the inclusion criteria: 1GTKI n=237, 2GTKI n=131. Patients initiating therapy with a 2GTKI had a 48% higher risk of treatment interruption versus patients initiating therapy with a 1GTKI (hazard ratio=1.48, 95% confidence interval 1.08-2.02). The time to treatment interruption was significantly longer in patients initiating therapy with a 1GTKI. Approximately 19% of patients had a regimen change, but there were no differences in rates of regimen changes between the two generations. Conclusions: In this study from a large single health plan population, treatment interruptions were more common among patients initiating therapy with a 2GTKI, yet regimen change rates did not vary by generation of TKI. Future research should assess reasons for treatment interruption and investigate these associations in other populations.