Clinical Trials

Inclusion Criteria:

• Man or woman greater than or equal to (>=) 18 years of age
• In Part 1, diagnosis of myelodysplastic syndrome (MDS) according to World Health Organization (WHO) criteria
• International Prognostic Scoring System (IPSS) low Risk or intermediate-1 risk MDS
• Red blood cell (RBC) transfusion dependent, defined as requiring at least 4 RBC units transfused over an 8-week period during the 16 weeks prior to Study Entry; pre-transfusion hemoglobin (Hb) should be less than or equal to 9.0 gram per deciliter (g/dL) to count towards the 4 units total
• Eastern Cooperative Oncology Group (ECOG) performance status 0, 1 or 2

Exclusion Criteria:

• Participant has known allergies, hypersensitivity, or intolerance to imetelstat or its excipients
• Participant has received an investigational drug or used an invasive investigational medical device within 30 days prior to Study Entry or is currently enrolled in an investigational study
• Prior treatment with imetelstat
• Have received corticosteroids greater than (>) 30 milligram per day (mg/day) prednisone or equivalent, or growth factor treatment within 4 weeks prior to study entry
• a) Prior treatment with a hypomethylating agent (example [eg], azacitidine, decitabine); b) Prior treatment with lenalidomide; c) Has received an erythropoiesis-stimulating agent (ESA) or any chemotherapy, immunomodulatory, or immunosuppressive therapy within 4 weeks prior to study entry (8 weeks for long-acting ESAs)