IMerge: imetelstat, a telomerase inhibitor, for transfusion-dependent lower-risk MDS after erythropoietin has failed
In IMerge, imetelstat, the first telomerase inhibitor to reach approval, freed about 40% of heavily transfused MDS patients from transfusions for eight weeks and 28% for six months, versus 15% and 3% with placebo.
IMerge randomised 178 patients with lower-risk, non-del(5q) MDS who were red-cell transfusion dependent and had relapsed after or were refractory to, or ineligible for, erythropoiesis-stimulating agents to intravenous imetelstat every four weeks or placebo (2:1). The primary endpoint was eight-week red-cell transfusion independence. This was achieved by 39.8% versus 15.0%; 24-week independence was 28.0% versus 3.3%, and responses lasted around a year with reductions in the SF3B1 mutant allele burden suggesting disease modification. Grade 3-4 thrombocytopenia and neutropenia were frequent but short-lived. Imetelstat was approved in 2024, the first drug in its class.
- 178 ESA-relapsed/refractory, transfusion-dependent, non-del(5q) lower-risk MDS patients; imetelstat vs placebo (2:1).
- 8-week transfusion independence 39.8% vs 15.0%; 24-week independence 28.0% vs 3.3%.
- Median duration of transfusion independence about one year in responders.
- Reductions in variant allele frequency of SF3B1 and other mutations in responders, suggesting disease-modifying activity.
- Grade 3-4 thrombocytopenia and neutropenia common (roughly two-thirds), usually resolving within 4 weeks.
IMerge validated telomerase as a drug target in cancer, decades after its discovery, and gave a second-line option for MDS patients whose anaemia no longer responds to erythropoietin or luspatercept. The hint of clonal reduction is what makes the drug interesting beyond transfusion counts. Cytopenias require close monitoring in the first cycles.
- Surrogate endpoint (transfusion independence) rather than survival or progression.
- High rates of grade 3-4 cytopenias in a population already at bleeding and infection risk.
- Only 8-week independence was the primary endpoint; the more meaningful 24-week rate was secondary.
- Disease-modifying claims rest on exploratory molecular analyses.
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