A Pilot Open-Label Study of the Efficacy and Safety of Imetelstat (GRN163L) in Patients With DIPSS_plus Intermediate-2 or High Risk Primary Myelofibrosis (PMF), Post-Polycythemia Vera Myelofibrosis (Post-PV MF), or Post-Essential Thrombocythemia Myelofibrosis (Post-ET-MF).

Inclusion Criteria:

- Diagnosis of one of the following:

- PMF per the revised World Health Organization (WHO) criteria

- Post-ET/PV MF per the IWG-MRT criteria

- High-risk or Intermediate-2 risk MF (as defined by the Dynamic International
Prognostic Scoring System [DIPSS-plus])

- Life expectancy of >= 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
upper limit of normal (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/uL

- Platelet count >= 50,000/uL

- 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 subjects 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 subjects 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

- Subjects with another active malignancy

- Note: patients 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 patient or compliance with
the protocol