Pacifica: A Randomized, Controlled Phase 3 Study of Pacritinib Vs. Physician's Choice in Patients with Primary Myelofibrosis, Post Polycythemia Vera Myelofibrosis, or Post Essential Thrombocytopenia Myelofibrosis with Severe Thrombocytopenia (Platelet Count <50,000/mL)

Background: Myelofibrosis (MF) is a life-limiting condition with severe morbidity in advanced stages. Patients with MF and severe thrombocytopenia (platelet counts <50,000/mL) have a particularly poor prognosis, with more frequent anemia and leukopenia, higher rates of hemorrhagic and thrombotic complications, and worse overall survival (~15 months) compared to the overall MF population (Scotch AH, et al, Leuk Res. 2017; Masarova L, et al, Eur J Haematol. 2018). Moreover, effective treatment options are limited in this high-risk population as the currently approved JAK inhibitor, ruxolitinib (RUX), is associated with treatment-related thrombocytopenia and often requires dose reductions for patients with platelet counts <100,000/mL, with reduced efficacy compared to patients able to tolerate higher doses. Further, there is no approved dose of RUX for patients with platelet counts <50,000/mL, and NCCN guidelines encourage physicians to consider clinical trials for such patients given the lack of approved therapies. Pacritinib (PAC) is an oral JAK2/IRAK1 inhibitor that has demonstrated clinical activity in MF patients in two prior Phase 3 studies (PERSIST-1, PERSIST-2) as well as a Phase 2 dose-finding study (PAC203), including patients with severe thrombocytopenia. The PACIFICA trial has been designed to evaluate the efficacy and safety of PAC 200 mg BID vs. physician's choice (P/C) therapy in patients with MF and severe thrombocytopenia.

Study Design and Methods: PACIFICA is a randomized, controlled Phase 3 trial of PAC vs. P/C in adult patients with primary or secondary MF who are not candidates for stem cell transplant, with DIPSS intermediate- or high-risk disease, ECOG PS ≤2, and platelet counts <50,000/mL, who have had up to 90 days of prior treatment with a JAK2 inhibitor or are JAK2 inhibitor-naïve. Additional exclusion criteria exist for patients with recent cardiac or hemorrhagic events, ejection fraction <50%, QTc >450 msec, or use of medications that increase the risk of hemorrhage or QT prolongation. On the PAC arm, patients receive continuous PAC 200mg BID. On the P/C arm, one of the following agents is selected prior to randomization: low-dose ruxolitinib (no more than 5 mg BID while platelet counts remain <50,000/mL), thalidomide, lenalidomide, corticosteroids, or hydroxyurea. The primary objective is to compare the efficacy of PAC vs. P/C based on the proportion of patients achieving a ≥35% spleen volume response (SVR) at Week 24. Secondary objectives include comparisons of the proportion of patients achieving a ≥50% reduction in total symptom score (TSS) at Week 24, overall survival, and proportion of patients who self-assess as "very much improved" or "much improved" as measured by the patient global impression of change (PGIC). Tertiary endpoints include alternative methods of evaluating SVR improvement, hematologic improvement (transfusion independence and improvement in anemia and thrombocytopenia), improvement in fatigue as measured by the PROMIS - Fatigue - Short form 7a, and changes in mutated allelic burden and gene expression (including correlation with response data). The study will enroll ~180 patients in a 2:1 ratio (PAC to P/C), which will have >80% power to achieve the primary endpoint. Enrollment is anticipated to begin in Q3 2019, as PACIFICA is expected to open as an amendment to the Phase 2 PAC203 study (NCT03165734) in select sites.