Imetelstat Demonstrates Survival Benefit in R/R Myelofibrosis Vs Real-World Data

An updated post hoc analysis from the phase 2 IMbark trial (NCT02426086) has reaffirmed that imetelstat (Rytelo), a first-in-class telomerase inhibitor, delivers a clinically meaningful and statistically significant overall survival (OS) benefit compared with best available therapy (BAT) in patients with JAK inhibitor–relapsed or refractory (R/R) intermediate-2 or high-risk myelofibrosis (MF), with results to be presented at the 2026 ASCO Annual Meeting.

For oncology nurses caring for patients with advanced myelofibrosis after JAK inhibitor failure, these findings may signal an important shift in what can be expected from subsequent therapy in a historically treatment-refractory population. At a median follow-up exceeding 4 years in both cohorts, imetelstat nearly doubled survival compared with BAT—a meaningful benchmark that nurses can use when counseling patients and families about prognosis and treatment planning in this high-risk setting.

In the primary comparison, which included 59 IMbark patients and 54 closely matched real-world patients from Moffitt Cancer Center who had discontinued ruxolitinib (Jakafi), median OS with imetelstat was 30.7 months (95% CI, 25.5–36.9) versus 15.4 months (95% CI, 13.1–30.5) with BAT, reflecting an approximately twofold improvement in survival (HR, 0.512; P = .003) in the unweighted analysis. The real-world dataset was expanded to 126 patients who received BAT at Moffitt between 2010 and 2025; propensity score weighting approaches were applied using 10 critical baseline covariates to minimize temporal confounding.

What should oncology nurses know about the survival findings from the IMbark trial?

The OS benefit observed with imetelstat in the IMbark analysis is particularly notable given the substantially improved real-world outcomes seen in the post-ruxolitinib population over the past decade. The Moffitt comparator dataset was purposefully constrained to patients diagnosed before 2016 who had relapsed or become refractory to ruxolitinib—the same eligibility criteria applied to IMbark—to ensure a closely matched, contemporaneous comparison and reduce bias from more recently diagnosed patients who inherently carry better outcomes.

For nurses involved in patient education, these findings offer a concrete framework for conversations about expectations after JAK inhibitor failure. Historically, patients with intermediate-2 or high-risk MF who progressed on JAK inhibitors faced median survival estimates of 13 to 16 months. The IMbark data, now supported by more than 4 years of follow-up, suggest that imetelstat can substantially extend that timeline in appropriately selected patients—a message that may meaningfully affect how patients and families approach treatment decisions and goals of care planning.

What is the background of the IMbark trial and this analysis presented at ASCO?

IMbark was a randomized, single-blind, multicenter phase 2 study evaluating 2 dose levels of imetelstat—9.4 mg/kg and 4.7 mg/kg administered intravenously once every 3 weeks—in patients with intermediate-2 or high-risk MF who had relapsed after or were refractory to JAK inhibitors. Primary end points included spleen volume response (≥35% reduction) and total symptom score response (≥50% reduction). The 9.4 mg/kg dose arm was subsequently advanced on the basis of more favorable efficacy and safety findings.

The post hoc OS analysis presented at the 2026 ASCO Annual Meeting incorporated 59 IMbark patients from the higher-dose arm and compared outcomes against a real-world BAT cohort of 54 closely matched patients identified from an expanded Moffitt Cancer Center database of 126 patients who had discontinued ruxolitinib between 2010 and 2025. IMbark enrollment criteria—including intermediate-2 or high-risk disease classification, prior ruxolitinib treatment, and relapsed or refractory status—were applied to the real-world dataset. Median follow-up was 46.2 months for IMbark patients and 48.2 months for the real-world comparator group.

For oncology nurses, awareness of the rigorous comparator methodology in this analysis may become increasingly important when discussing the evidence base for imetelstat with patients and multidisciplinary care team colleagues. The use of propensity score weighting and restricted eligibility criteria strengthens the reliability of the survival comparison—even as the broader real-world population continues to evolve.

How is imetelstat administered and what should nurses monitor?

Imetelstat is administered as an intravenous infusion at 9.4 mg/kg once every 3 weeks. The agent is FDA-approved for adults with low- to intermediate-1 risk myelodysplastic syndromes (MDS) with transfusion-dependent anemia requiring 4 or more red blood cell (RBC) units over 8 weeks; its use in relapsed/refractory MF is being evaluated in the ongoing phase 3 IMpactMF trial (NCT04576156).

Hematologic monitoring is central to nursing management of patients receiving imetelstat. Complete blood counts with differential should be assessed prior to each infusion cycle, with particular attention to platelet counts, hemoglobin, and absolute neutrophil count. Patients with MF already carry baseline cytopenias from their disease, which can compound treatment-related hematologic effects. Nurses should be alert to signs and symptoms consistent with thrombocytopenia, anemia, and neutropenia, and should have clear escalation pathways established within the clinical team before initiating therapy.

What safety risks should oncology nurses be prepared to manage?

The predominant toxicities associated with imetelstat across clinical trial experience are hematologic in nature. In IMbark, the most common grade 3 or higher adverse events were cytopenias—specifically thrombocytopenia, anemia, and neutropenia. Importantly, these events were typically manageable and short-lived, with most resolving to grade 2 or lower within 4 weeks. No major bleeding events or deaths due to thrombocytopenia were reported in the higher-dose arm of IMbark.

Dose reductions may be required for patients with significant hematologic toxicity, and oncology nurses play a critical role in capturing and escalating early signals before they progress. For patients with baseline thrombocytopenia—common in advanced MF—pre-infusion platelet assessments should be conducted systematically, and clinical teams should have dose-modification protocols accessible and clearly communicated to nursing staff.

For oncology nurses monitoring patients during and after infusion, it is also important to assess for signs of infusion-related reactions, though these were not among the predominant adverse events reported in the imetelstat MF trial data. The overall safety profile observed in IMbark was described as consistent with the known safety profile of the agent, reinforcing the feasibility of imetelstat in a heavily pretreated population. As this agent moves into the phase 3 setting through IMpactMF, nurses should remain engaged with emerging safety data and institutional protocol updates to optimize supportive care and monitoring practices for patients.

Reference

Kuykendall AT, et al. Updated overall survival analysis of imetelstat versus real-world best available therapy in patients with JAK inhibitor–relapsed/refractory myelofibrosis: IMbark trial and Moffitt Cancer Center real-world cohort comparison. To be presented at: 2026 American Society of Clinical Oncology Annual Meeting; May 29–June 2, 2026; Chicago, IL.