Adherence to Tyrosine Kinase Inhibitors Among Medicare Part D Beneficiaries with Chronic Myeloid Leukemia

Background: Tyrosine kinase inhibitors (TKIs) improve the survival of patients with chronic myeloid leukemia (CML) dramatically; however, nonadherence to TKI therapy may lead to resistance to the therapy. TKIs are very expensive and are covered under Part D insurance for Medicare patients. To the authors' knowledge, the impact of low-income subsidy status and cost sharing on adherence among this group has not been well studied in the literature.

Methods: Surveillance, Epidemiology, and End Results (SEER) registry data linked with Medicare Part D data from the years 2007 through 2012 were used in the current study. The authors identified 836 patients with CML with Medicare Part D insurance coverage who were new TKI users. Treatment nonadherence was defined as a binary variable indicating the percentage of days covered was <80% during the 180-day period after the initiation of TKI therapy. Logistic regression was used to examine the relationship between out-of-pocket costs per 30-day drug supply, Medicare Part D plan characteristics, and treatment adherence while controlling for other patient characteristics.

Results: Overall, 244 of the 836 patients with CML (29%) were nonadherent to targeted oral therapy during the 180 days after the initiation of treatment with TKIs. The multivariable logistic regression demonstrated that patients with heavily subsidized (odds ratio, 6.7; 95% confidence interval, 2.8-15.9) and moderately subsidized (odds ratio, 3.0; 95% confidence interval, 1.4-6.5) Medicare Part D plans were much more likely to demonstrate nonadherence compared with patients without a subsidy.

Conclusions: The current population-based study found a significantly higher rate of nonadherence among heavily subsidized patients with substantially lower out-of-pocket costs, which suggests that future research is needed to help lower the nonadherence rate among these individuals. Cancer 2018;124:364-73. © 2017 American Cancer Society.