Geron discontinues its Phase 3 IMpactMF trial of imetelstat after an independent committee determines it is unlikely to meet its overall survival endpoint.
Geron Corporation announced on October 28, 2026, that it would discontinue its Phase 3 IMpactMF clinical trial evaluating imetelstat in patients with relapsed or refractory myelofibrosis following Janus kinase (JAK) inhibitor treatment. The decision followed a recommendation from the trial’s independent Data Monitoring Committee (DMC), which advised that the study was unlikely to meet its primary endpoint of overall survival (OS).
The discontinuation represents a setback for Geron’s clinical development programme in myelofibrosis, where imetelstat was being investigated as a potential treatment option for patients with limited responses to prior JAK inhibitor therapy. However, the company reported no new safety signals that changed imetelstat’s known safety profile or required additional safety monitoring.
Geron plans to conduct a detailed analysis of the trial data and share the findings with the scientific community at a future date.
IMpactMF Evaluated Imetelstat in High-Risk Myelofibrosis
The IMpactMF trial (NCT04576156) was designed to evaluate whether imetelstat could improve overall survival in patients with intermediate-2 or high-risk myelofibrosis whose disease had relapsed or remained refractory following JAK inhibitor treatment.
This randomized, open-label, controlled Phase 3 study enrolled 327 patients, who were assigned in a 2:1 ratio to receive imetelstat or best available therapy (BAT). Patients in the imetelstat group received the telomerase inhibitor intravenously at a dose of 9.4 mg/kg every three weeks.
Overall survival was the primary endpoint, reflecting the trial’s central objective of determining whether imetelstat could provide a survival advantage over available treatment options in this patient population.
Secondary endpoints included symptom response, progression-free survival, spleen response, reduction in bone marrow fibrosis, and pharmacokinetic assessments. Symptom response was evaluated using changes in the total symptom score, including the proportion of patients achieving at least a 50% reduction at Week 24 compared with baseline.
The October 28 announcement did not disclose detailed findings for these secondary endpoints.
Why Did Geron Discontinue the Trial?
The decision followed the independent Data Monitoring Committee’s (DMC) assessment that IMpactMF was unlikely to meet its primary endpoint of overall survival. Based on this recommendation, Geron decided to discontinue the study.
However, the company has not released detailed survival estimates, hazard ratios, median survival figures, or comparative outcomes between the treatment groups. While the DMC’s assessment indicates that the trial was unlikely to achieve its predefined survival objective, the available information does not establish the magnitude of any treatment effect or explain the factors underlying the committee’s recommendation.
No New Safety Signals Reported
Alongside the discontinuation announcement, Geron confirmed that no new safety signals had emerged that changed imetelstat’s known safety profile or required additional safety monitoring.
This distinction indicates that the stated reason for discontinuation was the DMC’s assessment of the likelihood of meeting the primary efficacy endpoint rather than the identification of a new safety concern. However, the absence of new safety signals does not mean that imetelstat is free from adverse effects.
RYTELO Strategy Remains Focused on Lower-Risk MDS
Geron also reiterated its commitment to growing RYTELO demand in the United States and broadening access to eligible patients with lower-risk myelodysplastic syndromes (LR-MDS) outside the country.
RYTELO, which contains imetelstat, is approved in the United States and European Union for certain patients with LR-MDS. Its approved use in this indication is distinct from the investigation of imetelstat in relapsed or refractory myelofibrosis.
Therefore, the discontinuation of IMpactMF concerns the specific investigational setting and does not, by itself, change RYTELO’s approved status in MDS.
Clinical Interpretation
The discontinuation of IMpactMF highlights the challenges of demonstrating meaningful clinical benefit in late-stage development for patients with high-risk myelofibrosis following JAK inhibitor treatment. Although imetelstat was investigated as a potential treatment option in this setting, the independent DMC concluded that the trial was unlikely to meet its primary overall survival endpoint.
For Geron, the decision limits the clinical development opportunity for imetelstat in this myelofibrosis population, while the company’s commercial strategy remains centred on its approved LR-MDS indication.
The planned analysis of IMpactMF data will be important in understanding the clinical findings and the factors underlying the discontinuation decision. Until those results become available, the evidence supports a cautious conclusion: the trial’s primary survival objective was considered unlikely to be achieved, but the magnitude of any treatment effect and the broader clinical implications remain undetermined.
References
Geron Corporation Provides Update on Phase 3 IMpactMF Clinical Trial of Imetelstat in Relapsed/Refractory Myelofibrosis, Geron Corporation, 28 October 2026
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, ClinicalTrials.gov ID NCT04576156
About the Writer
Sravani Pamanji is a PharmD (LinkedIn) professional with experience in scientific writing, medical literature review, drug profile preparation, and clinical case documentation. She has contributed to scientific publication and presented at the 74th Indian Pharmaceutical Congress. Her training includes ICH GCP E6(R3), scientific research, and medication safety. She is passionate about evidence-based medical communication and accurate dissemination of clinical and pharmaceutical information.