A Single-Arm Multicenter Study to Assess the Efficacy, Safety, and Tolerability of Ropeginterferon alfa-2b-njft (P1101) in North American Adults With Essential Thrombocythemia

TPS7088 Background: Essential thrombocythemia (ET) is a myeloproliferative neoplasm (MPN) characterized by a high platelet count due to an overacting JAK-STAT pathway as a result of the most common mutations in JAK2, CALR and MPL genes. There is a high, unmet clinical need for safe and effective treatment options for patients with ET who require cytoreduction, both naïve and previously exposed to hydroxyurea (HU) or anagrelide (ANA). In addition to blood count control and thrombohemorrhagic risk reduction, treatment for ET should also halt/prevent disease progression to post-ET myelofibrosis. Reduction in variant allele frequency and changes in marrow morphology may lead to the elimination of the malignant clone, and treatment with an interferon may achieve this outcome. Interferons have been used in the treatment of MPNs for over 30 years with well-established improvements in hematological and molecular rates, but interferons are not approved by a regulatory agency for the treatment of ET. The objective of this study is to assess the efficacy of ropeginterferon alfa-2b-njft, a new generation interferon alfa, in adults with ET who live in the US or Canada. Methods: This single-arm, open-label study includes a 28-day screening period, a 12-month treatment phase, and a 28-day follow-up period, for a total trial duration of 14 months. An extension phase will supply ropeginterferon alfa-2b-njft to patients deriving benefit for a total of 3 years of treatment. Adults diagnosed with ET according to the WHO 2016 criteria with a platelet count at screening > 450 x 10 9 /L, cytoreductive treatment naïve, or with prior use or currently on HU and/or ANA may participate. Prior treatment with an interferon is an exclusion factor. Patients with a history or presence of clinically relevant depression, risk of suicide, or autoimmune disease may not participate. Ropeginterferon alfa-2b-njft will be administered subcutaneously every 2 weeks at the starting dose of 250 mcg (Week 0), 350 mcg (Week 2), and target dose of 500 mcg (Week 4) and remain fixed for the 12-month treatment period. Subjects currently on HU or ANA will follow a pre-specified dose-tapering schedule. All subjects will receive low-dose aspirin unless contraindicated. The primary endpoint is a durable response defined as the proportion of subjects who achieve simultaneous peripheral blood count remission (platelets ≤400 x10 9 /L and WBC < 10 x 10 9 /L) for at least 80% of bi-weekly measurements consecutively between weeks 32-52, a durable resolution of disease-related symptoms according to the MPN Symptom Assessment Form Total Symptom Score (MPN-SAF TSS), and absence of bleeding or thrombotic events. This study is being sponsored by PharmaEssentia USA. Clinical trial information: NCT05482971 .