Expanded Access for Treatment With Imetelstat

Key Inclusion Criteria: * Documented diagnosis of MDS according to World Health Organization (WHO) criteria confirmed by bone marrow aspirate and/or biopsy preferably within 24 but no more than 52 weeks prior to EAP start. * Very Low, Low, or Intermediate risk MDS (≤3.5) per IPSS-R. * Red blood cell (RBC) transfusion dependent, defined as requiring at least 4 RBC units over an 8-week period during the 16 weeks prior to EAP entry; pre-transfusion hemoglobin (Hb) should be less than or equal to 9.0 grams per deciliter (g/dL) to count towards the 4 units total. * Has MDS that has failed to respond or has lost response or are ineligible for ESAs. * To ensure participants have adequate iron stores they must have transferrin saturation greater than 20% and serum ferritin greater than 400 nanograms per milliliter (ng/mL). * Eastern Cooperative Oncology Group (ECOG) performance status score of 0, 1 or 2. * Hematology and biochemical laboratory test values within the protocol defined limits. * Have no approved alternative treatment available. * Inability to participate in a current imetelstat clinical study for the disease or conditions. * Have a treating physician who has appropriately evaluated the benefit/risk profile for potential imetelstat treatment. Key Exclusion Criteria: * Have previously assessed as having IPSS-R high or very high risk MDS. * Participant with del(5q) karyotype. * Participant with MDS/myeloproliferative neoplasm Overlap Syndromes. * Participant has known allergies, hypersensitivity, or intolerance to imetelstat or its excipients. * Participant has received an experimental or investigational product or used an invasive investigational medical device within 30 days prior to EAP entry or is currently enrolled in an investigational study. * Prior treatment with imetelstat; or eligible for enrollment in an ongoing imetelstat clinical trial. * Prior treatment with lenalidomide or a hypomethylating agent (example, azacitidine, decitabine, or decitabine/cedazuridine). * Has received an ESA or any anti-MDS therapy, chemotherapy, immunomodulatory, or immunosuppressive therapy within 4 weeks prior to EAP entry. * Prior history of hematopoietic stem cell transplant. Note: Other protocol specified inclusion/exclusion criteria may apply.