Phase 2 Study to Evaluate Activity of 2 Dose Levels of Imetelstat in Participants with Intermediate-2 or High-Risk Myelofibrosis (MF) Previously Treated With a Janus Kinase (JAK) Inhibitor

This clinical trial is being conducted by Janssen Research & Development (Janssen) under the terms of an exclusive worldwide license and collaboration agreement with Geron. The first patient in the IMbark study was dosed in September 2015.

Study Design

IMbark is a Phase 2, randomized, single-blind and multi-center study originally designed to evaluate two dosing regimens of imetelstat administered as a single agent to participants with intermediate-2 or high risk MF whose disease is relapsed after or refractory to JAK inhibitor treatment. The study consists of three stages: a screening phase, a treatment phase and a follow-up phase. Participants receive imetelstat at either 9.4 mg/kg (if enrolled in Arm 1) or 4.7 mg/kg (if enrolled in Arm 2) given intravenously every 3 weeks until disease progression, unacceptable toxicity, or study end. Imetelstat will be evaluated by  spleen response and symptom response. 

Current Status

Enrollment of new participants is currently suspended following a planned internal data review. Participants already enrolled in Arm 1 (9.4 mg/kg) may continue to receive imetelstat, and enrollment may be resumed after a second internal data review that is planned by the end of the second quarter of 2017. Participants already enrolled in Arm 2 (4.7 mg/kg) may continue with their current imetelstat dose or have it increased to 9.4 mg/kg at the investigator's discretion. Enrollment in Arm 2 will not resume. To learn more about this study, including enrollment criteria, locations and current status, visit

Imetelstat, a telomerase inhibitor, is an investigational treatment for cancer and has not been approved by the FDA or any other regulatory agency.