Adverse Events Among Patients with Hairy Cell Leukemia Treated with Purine Nucleoside Analogs in the United States

Introduction: Purine nucleoside analogs (PNAs) are the recommended first-line treatment in patients with hairy cell leukemia (HCL) owing to their efficacy. However, because of the rarity of this disease, little is known about clinically significant adverse events (AEs) outside of previously performed clinical trials. This retrospective claims-based study of patients treated in the current era of improved supportive care assessed the incidence and prevalence rates of AEs associated with PNA use and healthcare resource utilization (HRU) among patients with HCL enrolled in the Truven MarketScan Commercial Claims and Encounters and the Medicare Supplemental databases. Methods: Adults (≥18 years old) diagnosed with HCL (≥2 medical claims ≥30 days apart) between January 1, 2006 and December 31, 2015 were included in the study. All patients had ≥1 claim for PNA therapy (cladribine or pentostatin ± rituximab) after the HCL diagnosis date and the 1st prescription claim was defined as the index date. Continuous health plan enrollment for ≥6 months pre- (baseline period) and ≥12 months post-index date (follow-up period) was required. Patients treated with a PNA during the baseline period were excluded. Incidence rate was defined as the number of new cases of an AE during the follow-up period divided by the number of patients at risk (patients without any evidence of the adverse event in the 6-month baseline period). Prevalence rate was defined as the number of all AEs (existing cases during the baseline period and new cases during the follow-up period) divided by the total number of patients. Incidence and prevalence rates were calculated as rate per 1000 patient-years at risk. To evaluate the HRU, PNA-treated patients with HCL were categorized based on occurrence of highest AE during the follow-up period. Generalized linear model (GLM) compared HRU during the 12-month follow-up, adjusting for demographic, clinical characteristics, and baseline total healthcare costs. Results: In total, 647 PNA-treated patients with HCL were identified. Mean age (standard deviation) was 57.1 (12.2) years. Most patients were men (81.5%) and resided in the southern USA (32.2%). Over the 12-month follow-up period, 87.2% of the PNA-treated patients developed at least one AE. PNA-related AEs with the highest incidence rate were myelosuppression, anemia, and skin toxicities. The prevalence rate showed a similar trend for PNA-related AEs. Infectious complications including opportunistic inf