Ruxolitinib in clinical practice for therapy of myelofibrosis: Single USA center experience following Food and Drug Administration approval

Abstract

Myelofi brosis is a myeloproliferative neoplasm (MPN) characterized by increased bone marrow fi brosis, abnormal blood counts with peripheral cytopenias, extramedullary hematopoiesis, splenomegaly and profound constitutional symptoms [1,2]. Presenting as a primary disease or arising from polycythemia vera or essential thrombocythemia, myelofi brosis incurs a signifi cant symptom burden for patients, and results in a reduced survival of 2 – 11 years [3 – 7]. Amongst MPNs, myelofi brosis has represented a unique challenge to eff orts aimed at palliating symptoms or impacting disease course. Th e 2005 discovery of the gain-of-function JAK2V617F mutation present in a signifi cant proportion of patients with polycythemia vera, essential thrombocythemia and myelofi brosis opened a new avenue of investigation into potential novel therapies [8,9]. Among the various JAK2 inhibitor agents that have been developed, ruxolitinib was the fi rst to receive Food and Drug Administration (FDA) approval in the USA for the treatment of intermediate- and high-risk myelofi brosis. Th e Controlled Myelofi brosis Study with Oral JAK Inhibitor Treatment Trials compared ruxolitinib therapy in patients with intermediate-2 or high-risk myelofi brosis with placebo (COMFORT-I) and with best available therapy (COMFORT-II) [10,11]. In both trials, patients in the ruxolitinib group experienced signifi cant clinical benefi ts, including reduction in spleen size and amelioration of debilitating symptoms coupled with a tolerable side-eff ect profi le. In this study, we report the initial clinical experience with ruxolitinib outside of the clinical trial setting at our high-volume MPN program. Approval for the analysis was obtained from the Mayo Clinic Institutional Review Board. Patients with myelofi brosis including primary myelofi brosis (PMF), post-polycythemia vera (post-PV MF) and post-essential thrombocythemia (post-ET MF) were included. All patients had a Dynamic International Prognostic Scoring System (DIPSS) score of intermediate-1/2 risk or high risk at the start of therapy [12]. Clinical and hematopathological data, including bone marrow biopsy, were reviewed in all cases, and the diagnosis was made in accordance with the 2008 World Health Organization criteria. Baseline patient information, physical examination results, laboratory data, hematopathology reports and interim follow-up information were acquired via chart review, with baseline obtained within 1 month of initiating therapy. All patients were prescribed ruxolitinib within 6 months of FDA approval. Ruxolitinib was started at 20 mg twice daily for patients with platelet counts of 200 10 9 /L or hemoglobin concentrations 10 g/dL. Patients with values below these were started on lower doses at the discretion of the providing physician. Doses were adjusted for lack of effi cacy or excess toxicity. Complete blood counts were checked on a weekly basis for the fi rst 2 months, then monthly thereafter. Drug effi cacy and toxicity were determined at follow-up visits and through telephone conversations with patients. Symptoms were assessed through a verbal response during review of systems questioning. Spleen size was determined by physical examination. Descriptive statistics were determined using means, medians, ranges and standard deviations for continuous variables. Categorical variables were evaluated using frequencies and relative frequencies.