Clinical Benefit of Ropeginterferon Alfa 2b (P1101) in Patients with Myelofibrosis

Background:

Myelofibrosis (MF) is a clonal bone marrow disorder characterized by a constitutional symptoms, splenomegaly, anemia, elevated WBC and bone marrow fibrosis. Ruxolitinib is a JAK2 inhibitor approved for patients with Intermediate-2 (INT-2) or high risk disease based on dynamic international prognostic scoring system (DIPSS)), however, there are limited options for patients with early disease. Interferon alpha (IFNa) is a cytokine therapy that has been used in treatment of chronic myelogenous leukemia and polycythemia vera (PV). In these diseases, there can be a reduction in the clonal burden in addition to a hematologic response. Therefore, we sought to use this therapy in patients with MF.

Methods:

Patients who had MF were enrolled on an IRB approved clinical protocol in a single arm, single institution study. Patients were stratified to either an early disease arm (characterized by intermediate 1 (INT-1) risk or advanced disease (Int-2 or high risk disease based on DIPSS). Patients were started on Ropeginterferon alfa 2b (P1101) at 50 ug every two weeks, and the dose was titrated up to either 300 ug every other week, or unacceptable toxicity. Patients were monitored for response based on international working group criteria.

Results:

Demographics: Eight patients with MF have been enrolled on the study to date (Early: 2, Int/High: 6). Median age was 69.5 (45 - 88), five patients were female. Five patients had primary MF (PMF) and 3 had post-essential thrombocythemia or post PV MF. Three patients had previous treatment for their disease. Four patients continue to receive active treatment (2 early disease, and 2 advanced disease), and for those who remain on treatment, they range from 7 - 29 cycles.

Efficacy: Three patients experienced a clinical improvement (1 based on MPN-SAF total symptom score, and 2 based on reduction of spleen size). Both early stage patients have had a CI based on spleen responses as their best response and currently remain on treatment. The remaining 2 who are on therapy had stable disease. Those who remain on therapy have been receiving treatment for 7-29 cycles with continued response.

Toxicity: A grade 3 adverse event (AE) potentially attributable to the treatment occurred in 4 patients (50%), 3 (37.5%) patients had anemia, and 2 (25.0%) patients had lymphopenia. Only one patient discontinued therapy due to AEs (dizziness, atrial fibrillation). Reasons for stopping include disease progression (1), toxicity (1) and lack of benefit (2). The median number of cycles for those who ended treatment was 8 (4-10). No deaths have occurred.

Discussion:

P1101 appears to be a well-tolerated therapy that has shown a durable clinical improvement in 37.5% in a small study. These results, along with historic data suggesting possible reduction in clonal burden, suggest that ongoing studies are warranted to further understand the clinical benefit of P1101 in MF.

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