RecruitingPhase 1Drug trialA Phase 1 Study of PRT12396 in Participants With Select Myeloproliferative NeoplasmsThis is a first-in-human, open-label, multi-center Phase 1 study designed to evaluate the safety, tolerability, pharmacokinetics, and preliminary efficacy of PRT12396 in participants with high-risk polycythemia vera (PV) and myelofibrosis (MF), and to determine the maximum tolerated dose (MTD) and recommended dose(s) for expansion (RDE\[s\]). The study consists of a dose-escalation phase followed by a dose-expansion phase to further evaluate selected dose level(s).