Phase 2 Clinical Trial 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 was originally conducted by Janssen Research and Development (Janssen) under a collaboration agreement (see Partners). Geron assumed responsibility for this clinical trial in May of 2019. 

Study Design

IMbark was designed as a Phase 2 clinical trial to evaluate two starting dose levels of imetelstat (either 4.7 mg/kg or 9.4 mg/kg administered by intravenous infusion every three weeks) in approximately 200 patients with Intermediate-2 or High-risk MF who have relapsed after or are refractory to prior treatment with a JAK inhibitor. IMbark was originally conducted by Janssen.

The co-primary efficacy endpoints for the trial are spleen response rate and symptom response. Key secondary endpoints are safety and overall survival.

Current Status

More than 100 patients were enrolled. The first patient in the IMbark trial was dosed in September 2015. The trial is now closed to new patient enrollment and has entered an extension phase to enable patients remaining on treatment to continue to receive imetelstat treatment, per investigator discretion. During the extension phase standard data collection will primarily consist of safety information.

The IMbark protocol-specified primary analysis, which included an assessment of overall survival, or OS, coincided with the protocol-specified final analysis for the trial, which resulted in a primary/final analysis and is referred to as the primary analysis. The results of the primary analysis and updated data on OS were presented at the American Society of Hematology Annual Meeting in December 2018.

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.