Imetelstat Sodium in Treating Participants With Primary or Secondary Myelofibrosis

Inclusion Criteria:

Diagnosis of one of the following:
Primary myelofibrosis (PMF) per the revised World Health Organization (WHO) criteria.
Post-polycythemia vera/essential thrombocythemia myelofibrosis (Post-ET/PV MF) per the International Working Group for Myeloproliferative Neoplasms Research and Treatment (IWG-MRT) criteria.
High-risk or Intermediate-2 risk MF (as defined by the Dynamic International Prognostic Scoring System [DIPSS-plus]).
Life expectancy of greater than or equal to (>=) 12 weeks.
Able to provide informed consent and be willing to sign an informed consent form.
Eastern Cooperative Oncology Group (ECOG) performance status of 0, 1 or 2.
Serum glutamic oxaloacetic transaminase (SGOT) (aspartate aminotransferase [AST]) =<2.5 x upper limit of normal (ULN) (or =<5 x ULN if in the investigator's opinion the elevation is due to extramedullary hematopoiesis).
Serum glutamic pyruvate transaminase (SGPT) alanine aminotransferase (ALT) =<2.5 x ULN (or =<5 x ULN if in the investigator's opinion the elevation is due to extramedullary hematopoiesis).
Total bilirubin =<3.0 mg/dL (or direct bilirubin < 1 mg/dL).
Creatinine =<3.0 mg/dL.
Absolute neutrophil count >=1000/microliter (mcL).
Platelet count >=50,000/mcL.
Absence of active treatment with systemic anticoagulation and a baseline prothrombin time (PT) and activated partial thromboplastin time (aPTT) that does not exceed 1.5 x ULN.
Females of childbearing potential must have a negative pregnancy test =<7 days prior to registration, unless they are surgically sterile for at least 3 months (i.e., hysterectomy), OR postmenopausal for at least 12 months (follicle-stimulating hormone [FSH] >30 U/mL).
Females of childbearing potential must agree to take appropriate precautions to avoid pregnancy (with at least 99% certainty) from screening through end of study; permitted methods for preventing pregnancy must be communicated to study participants and their understanding confirmed.
Males must agree to take appropriate precautions to avoid fathering a child (with at least 99% certainty) from screening through follow-up; permitted methods for preventing pregnancy should be communicated to the participants and their understanding confirmed.

Exclusion Criteria:

Females who are pregnant or are currently breastfeeding.
Any chemotherapy (e.g., hydroxyurea), immunomodulatory drug therapy (e.g., thalidomide), immunosuppressive therapy, corticosteroids > 10 mg/day prednisone or equivalent, growth factor treatment (e.g., erythropoietin) or Janus kinase (JAK) inhibitor therapy =<14 days prior to registration.
Participants with another active malignancy.
Note: participants with early stage squamous cell carcinoma of the skin, basal cell carcinoma of the skin or cervical intraepithelial neoplasia are eligible for enrollment.
Known positive status for human immunodeficiency virus (HIV).
Any unresolved toxicity greater or equal to grade 2 from previous anticancer therapy, except for stable chronic toxicities not expected to resolve.
Incomplete recovery from any prior surgical procedures or had surgery =<4 weeks prior to registration, excluding the placement of vascular access.
Presence of acute active infection requiring antibiotics.
Uncontrolled intercurrent illness or any concurrent condition that, in the Investigator's opinion, would jeopardize the safety of the participant or compliance with the protocol.