Burden of Disease and Clinical Responses in Low and Intermediate-1 Risk Myelofibrosis Patients Treated with Ruxolitinib

Myelofibrosis (MF) is a hematologic neoplasm characterized by variable degrees of cytopenias/ myeloproliferation, extramedullary hematopoiesis, disease-related constitutional symptoms and an increased risk for acute myeloid leukemia (AML) transformation. Ruxolitinib, a JAK1/2 inhibitor is FDA approved for the management of intermediate to high-risk MF. However, intermediate-2 and high-risk MF patients accounted for 99% of patients (pts) in the 2 pivotal trials that led to the approval of ruxolitinib in North America, Australia and Europe (COMFORT 1 and COMFORT 2 studies). However, even low and intermediate-1 (int-1) risk MF pts could have a high burden of disease. Here we report our experience of using ruxolitinib in MF pts stratified as low and int-1 risk by the Dynamic International Prognostic Scoring System (DIPSS). A total of 25 pts with low and Int-1 risk disease were treated with ruxolitinib at the Cleveland Clinic and Northwestern University. The median age of the cohort was 61 yrs (range=33-87; males=9, females=16). The median total symptom score (TSS) by Myeloproliferative Neoplasm Symptom Assessment

Form (MPN SAF) was 20. The median pre-treatment spleen size by palpation was 13 cm below the left costal margin. Baseline median bone marrow (BM) fibrosis grading was 2 (on a scale 0-3; grade 1 N=3, grade 2 N=11, and grade 3 N=11). The indications for starting ruxolitinib were constitutional symptoms (fatigue N=20, night sweats N=4, pruritus N=1) and splenomegaly (N=13). The median starting dose was 5 mg twice daily, 10mg twice daily at 3 months and 6 months, and 5mg twice daily at 12 months. The median dose at last follow up was 10 mg twice daily. The median duration of treatment was 12 months. There was a median 73% reduction in the MPN SAF TSS compared to baseline (P< 0.001). There was improvement in each of the parameters of the TSS. The percentage of reduction in spleen size by palpation at 3, 6, 12 months was 49, 57, and 64%, respectively. In 5 patients who had a repeat BM biopsy, there was an improvement in their BM fibrosis by at least 1 grade (N=3), stable fibrosis (N=1) or increased fibrosis (N=1). Hematologic adverse events were reported at 3, 6, 12 months of treatment. Using Common Terminology Criteria for Adverse Events (CTCAEv4.0), there were seven with grade 3/4 anemia and six with grade 3/4 thrombocytopenia. Non-hematologic adverse events reported at 3, 6, 12 months of treatment included dizziness (N=1), headaches (N=1) and infections (pneumonia N=2, cellulitis N=2, perineal abscess N=1, Herpes Zoster N=2, and gluteal abscess after BM biopsy N=1; only one required hospitalization). Ruxolitinib was discontinued in 5 patients due to lack of clinical response (N=3) and grade 3/4 anemia/thrombocytopenia (N=2). The remaining 20 patients are still on treatment. None of the pts progressed to AML or died. The median follow up of our cohort was 27 months. Further, using a multi-Analyte ELISArray Kit, plasma concentrations of interleukins (IL):IL1A, IL1B, IL2, IL4, IL6, IL8, IL10, IL12, IL17A, INFg, TNFa and GM-CSF were measured in low/int-1 risk pts (N=3) and intermediate-2/high risk patients (N=4) and no statistically significant difference was found between the two risk groups (P>0.05) further supporting the high burden of disease observed even in low and int-1 risk MF patients. In conclusion, pts with low/int-1 risk MF have a high burden of disease and can achieve meaningful clinical responses to ruxolitinib similar to int-2/ high risk MF pts without severe toxicity. Larger studies are needed to further evaluate the safety and efficacy of ruxoltinib in this patient population.