Inclusion Criteria:

ET-Specific Criteria

- Confirmed diagnosis of ET by WHO criteria

- Patients with ET requiring cytoreduction who have failed or are intolerant to at
least one prior therapy, or who refuse standard therapy

- Laboratory criteria (within 14 days of first study drug administration):

- Platelets > 600,000/μL

- ANC ≥ 1500/μL

- Hemoglobin ≥ 10 g/dL

PV-Specific Criteria

- Confirmed diagnosis of PV by WHO criteria

- Patients with PV requiring cytoreduction with phlebotomy and/or myelosuppressive
agents

- Patients may have failed or are intolerant to at least one prior therapy, or
refuse standard therapy

- For those patients receiving phlebotomy only, the frequency over the past year
must be at least one phlebotomy every 3 months.

- Undergone phlebotomy and attained a Hct < 47% (men) or < 45% (women) (or
pre-specified Hct count that is tolerable) within 14 days prior to the start of study
treatment

- Cessation of myelosuppressive agents prior to initiation of study treatment (unless
approved by Geron Medical Monitor for unusual circumstances)

- Hydroxyurea or anagrelide: Cessation 1 day prior to initiation of study
treatment. Consideration to the timing of cessation of this therapy prior to
the start of study treatment should take into account the requirement for
phlebotomy.

- INF-α or pegylated- INF-α: Cessation 4 weeks prior to initiation of study
treatment

- Laboratory criteria (within 14 days of first study drug administration):

- Platelets > the lower limit of normal (LLN)

- ANC ≥ 1500/μL

General Criteria (All Patients)

- Willing and able to sign an informed consent

- Male or female, aged 18 years or older

- ECOG performance status 0-2

- Laboratory criteria (within 14 days of first study drug administration):

- INR (or PT) and aPTT < 1.5 x the upper limit of normal (ULN)

- Serum creatinine ≤ 2 mg/dL

- Serum bilirubin < 2.0 mg/dL (patients with Gilbert's syndrome: serum bilirubin <
3 x ULN)

- AST (SGOT) and ALT (SGPT) ≤ 2.5 x ULN

- Alkaline phosphatase < 2.5 x ULN

- Any clinically significant toxicity from previous cancer treatments and/or major
surgery must have recovered to Grade 0-1 prior to initiation of study treatment

- Women of childbearing potential must have a negative pregnancy test and agree to use
effective birth control during and for at least 12 weeks after the last study
treatment with imetelstat

- Male patients must agree to use effective birth control for themselves or their
partner during and for 12 weeks after the last study treatment with imetelstat.

Exclusion Criteria

Patients who meet any of the following criteria will be excluded from screening and study
entry:

- Women who are pregnant or breast feeding

- Prior stem cell transplantation

- Investigational therapy within 4 weeks prior to first study drug administration

- Clinically significant cardiovascular disease or condition including:

- Uncontrolled congestive heart failure (CHF)

- Need for anti-arrhythmic therapy for a ventricular arrhythmia

- Clinically significant severe conduction disturbance per the Investigator's
discretion

- Ongoing angina pectoris requiring therapy

- New York Heart Association (NYHA) Class II, III, or IV cardiovascular disease
(see Appendix E)

- Known positive serology for human immunodeficiency virus (HIV)

- Serious co-morbid medical conditions, including active or chronically recurrent
bleeding, clinically relevant active infection, cirrhosis, and chronic obstructive or
chronic restrictive pulmonary disease per the Investigator's discretion

- Any other severe, acute, or chronic medical or psychiatric condition, laboratory
abnormality, or difficulty complying with protocol requirements that may increase the
risk associated with study participation or study drug administration or may
interfere with the interpretation of study results and, in the judgment of the
Investigator, would make the patient inappropriate for this study.