Background: Current treatment options for red blood cell (RBC) transfusion-dependent (TD) patients (pts) with lower risk (LR) myelodysplastic syndromes (MDS) relapsed after or refractory to erythropoiesis-stimulating agents (ESAs) have limited efficacy and durability; new approaches are needed. Imetelstat is a first-in-class telomerase inhibitor that targets cells with short telomeres and active telomerase, characteristics observed in MDS pts across all disease stages. IMerge (MDS3001) is a Phase 2/3 global study of imetelstat for TD pts with non-del(5q) LR MDS post ESA therapy. The results from Phase 2 part indicated that imetelstat achieved durable RBC transfusion independence (RBC-TI) and the most frequently reported adverse events were manageable and reversible grade ≥3 cytopenias. Among 38 pts with median follow-up of 24 months, 8-week, 24-week and 1-year TI rates were 42%, 32% and 29%, respectively; these responses were seen across different LR MDS subtypes. Median TI duration was 20 months and the longest TI was 2.7 years. A high and durable hematologic improvement-erythroid (HI-E) rate of 68% for a median duration of 21 months were also achieved. Reduction of variant allele frequency of mutations by imetelstat treatment was observed in some pts and correlated with clinical benefits (Platzbecker et al EHA 2020; Steensma et al JCO 2020). These results support the Phase 3 part of the trial. Methods: IMerge is two-part, Phase 2/3 study (ClinicalTrials.gov: NCT02598661). The Phase 3 part of the study is open for enrollment to adult pts with International Prognostic Scoring System (IPSS) low or intermediate-1 risk, non-del(5q) MDS who are TD, are relapsed after or refractory to ESAs, and have not received treatment with lenalidomide or hypomethylating agents. The study is a randomized (2:1) double-blind, placebo-controlled trial to compare efficacy of imetelstat vs placebo that will enroll approximately 170 pts and will be conducted at approximately 120 centers in North America, Europe, Asia and Middle East. Imetelstat is administered as 2-hour IV infusion every 4 weeks at 7.5 mg/kg. The primary endpoint of the study is to assess the rate of RBC-TI lasting ≥8 weeks. Secondary endpoints include safety, rate of RBC-TI ≥24 weeks, time to RBC-TI start, RBC-TI duration, rate of HI-E, the amount and relative change in RBC transfusions, rate of CR or PR, overall survival, progression of MDS, pharmacokinetics, and quality of life. Biomarkers relevant to the mechanism of action of imetelstat will be assessed to demonstrate target inhibition and their association with clinical responses. Cytogenetics and mutation analyses will be performed to evaluate the impact of imetelstat on reduction/depletion of malignant clones leading to disease modification. The study is currently recruiting pts. Clinical trial information: NCT02598661