A Study Comparing Imetelstat Versus Best Available Therapy for the Treatment of Intermediate-2 or High-risk Myelofibrosis (MF) Who Have Not Responded to Janus Kinase (JAK)-Inhibitor Treatment

The purpose of the study is to evaluate the overall survival of participants treated with imetelstat compared to best available therapy with intermediate-2 or high-risk Myelofibrosis (MF) who are relapsed/refractory (R/R) to Janus Kinase (JAK)-Inhibitor treatment.

This is a multicenter study with 2 arms, and will include 3 phases: a) screening phase of up to 28 days before randomization during which participants will complete a 14-day washout period from all prior therapies including JAK-inhibitor treatment, and the participant's eligibility will be reviewed; b) treatment phase, from randomization until study treatment (imetelstat or BAT) discontinuation; and c) post treatment follow-up phase, that begins when the participant discontinues treatment, and will continue until death, lost to follow-up, withdrawal of consent, or study end, whichever occurs first. Participants will be randomized (2:1) into 2 Arms (Arm A will receive imetelstat and Arm B will receive BAT). Participants who meet progressive disease criteria and discontinue BAT, may crossover to receive imetelstat treatment after sponsor's approval.