Geron Corporation has opted to discontinue a late-stage trial evaluating its rare blood cancer drug Rytelo (imetelstat) after a forecasted efficacy miss.
The California-based biotech hit stop on the Phase III IMpactMF trial (NCT04576156) based on a recommendation from the independent data monitoring committee, which noted that Rytelo was unlikely to meet the trial’s primary endpoint by offering significant improvements to overall survival (OS).
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Geron enrolled patients with intermediate-2 or high-risk myelofibrosis who were relapsed or refractory to a JAK inhibitor. JAK inhibitors are standard of care (SoC) in this patient population. The study had enrolled 327 patients across 144 locations, as per ClinicalTrials.gov.
Though the data monitoring committee deemed it unlikely that Rytelo would demonstrate sufficient efficacy in myelofibrosis, researchers did find the drug to be safe for use in this patient population, as there were no new safety signals linked to the drug’s use.
“Given the recommendation from the DMC, we believe discontinuing our Phase III IMpactMF trial at this time is the right course of action,” commented Geron’s CMO and EVP of R&D, Joseph Eid, adding that the company will now thoroughly evaluate the data and share insights to inform future myelofibrosis research.
Myelofibrosis is a rare type of blood cancer that causes the buildup or scar tissue inside the bone marrow, thus disrupting the normal production of blood cells. Of the one in 500,000 worldwide who live with this disease, many experience fatigue and joint pain, while the condition can also be associated with a shortened lifespan.
Improving outcomes in myelofibrosis
While IMpactMF’s termination will be a notable setback for Geron’s Rytelo pipeline, the biotech will now look ahead to the drug’s combinatory potential alongside Incyte and Novartis’ JAK inhibitor Jakafi (ruxolitinib) in frontline myelofibrosis, which is currently being evaluated in the Phase I IMproveMF trial.
Currently, Jakafi, known as Jakavi outside of the US, dominates the myelofibrosis market, with the drug having generated $5.2bn in sales during 2025. Neither Novartis or Incyte have disclosed what proportion of these sales were myelofibrosis related. Jakafi was approved by the US Food and Drug Administration (FDA) to treat intermediate- or high-risk myelofibrosis in 2011.
Meanwhile, Rytelo is comparatively new to the myelofibrosis treatment landscape as the drug was originally approved by US regulators as a therapy for erythropoiesis stimulating agent-unresponsive or ineligible lower risk myelodysplastic syndrome in 2024.
Analysts at GlobalData, parent company of Clinical Trials Arena, currently forecast a blockbuster future for Rytelo, with expectations the drug will pull in sales of $1.2bn in 2032.
There are also other drugs making their way through the clinical pipeline in myelofibrosis at the moment. This includes Karyopharm’s exportin-1 inhibitor Xpovio (selinexor), which demonstrated its potential to offer additive benefits to SoC in JAK inhibitor-naïve myelofibrosis at this year’s American Society of Clinical Oncology (ASCO) congress.
Meanwhile, Eli Lilly’s type 2 JAK2 inhibitor AJ1-11095 showed encouraging efficacy and safety in a Phase I trial. Lilly originally acquired the rights to AJ1-11095 through its takeover worth up to $2.3bn of Ajax Therapeutics.
