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.  Key secondary endpoint includes overall survival.

Current Status

The study is closed to further participant enrollment. More than 100 patients have been enrolled. Participants already enrolled in Arm 1 (9.4 mg/kg) may continue to receive imetelstat. 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. 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.