The following criteria is provided for health care professionals.
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.