Phase II Imetelstat in Intermediate-2 / High-Risk MF Relapsed/Refractory to Janus Kinase Inhibitor

Inclusion Criteria:

* Diagnosis of primary myelofibrosis (PMF) according to the revised WHO criteria; or post-essential thrombocythemia-myelofibrosis (PET-MF) or post-polycythemia vera-myelofibrosis (PPV-MF) according to the International Working Group-Myeloproliferative Neoplasms Research and Treatment (IWG-MRT) criteria.
* Dynamic International Prognostic Scoring System (DIPSS) intermediate-2 or highrisk MF.
* Measurable splenomegaly prior to study entry as demonstrated by palpable spleen measuring ≥ 5 cm below the left costal margin OR spleen volume of ≥ 450 cm\^3 measured by magnetic resonance imaging (MRI).
* Active symptoms of MF as demonstrated by a symptom score of at least 5 points (on a 0 to 10 scale) on at least one of the symptoms or a score of 3 or greater on at least 2 of the symptoms.
* Documented progressive disease during or after Janus kinase (JAK) inhibitor therapy.
* Eastern Cooperative Oncology Group (ECOG) performance status 0, 1 or 2.

Exclusion Criteria:

* Peripheral blood blast count of ≥ 10% or bone marrow blast count of ≥ 10%.
* Prior treatment with imetelstat.
* Any chemotherapy or MF-directed therapy, investigational drug, hydroxyurea, immunomodulatory or immunosuppressive therapy, corticosteroids or JAK inhibitor therapy ≤14 days prior to randomization.
* Major surgery within 4 weeks prior to randomization.
* Active systemic hepatitis infection requiring treatment (carriers of hepatitis virus are permitted to enter the study), of any type or known acute or chronic liver disease including cirrhosis.
* Prior history of hematopoietic stem cell transplant.