Extension Study Evaluating the Long Term Safety and Efficacy Study of CYT387 in Primary Myelofibrosis (PMF) or Post-polycythemia Vera (PV) or Post-essential Thrombocythemia (ET)

Inclusion Criteria: * Patients must have completed at least 9 cycles of treatment on the core study 'A Phase I/II, Open-Label, Dose-Escalation Study Evaluating the Safety, Tolerability, Pharmacokinetics and Pharmacodynamics of Orally-Administered CYT387 in Primary Myelofibrosis or Post-Polycythemia Vera or Post-Essential Thrombocythemia Myelofibrosis (CCL09101)' and achieved stable disease (SD), clinical improvement (CI), partial remission (PR) or complete remission (CR) using the International Working Group consensus criteria for treatment responses in myelofibrosis with myeloid metaplasia (IWG-MRT; Tefferi et al., 2006) * Must be able to provide informed consent and be willing to sign an informed consent form. * Must have an Eastern Cooperative Oncology Group (ECOG) performance status of 0, 1 or 2. * Must have evidence of acceptable organ function within 7 days of initiating study drug as evidenced by the following: * SGOT (AST) or SGPT (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) * Bilirubin \<= 2.0 x ULN or direct bilirubin \< 1.0 * Serum creatinine \<= 2.5 x ULN * Absolute neutrophil count \>= 500/µL * Platelet count \>= to 20,000/µL * Females of childbearing potential must have a negative pregnancy test within 4 days of entering the extension protocol. Exclusion Criteria: * A delay of 4 weeks or more since the last preceding dose of CYT387 on the CCL09101 core study. * Any chemotherapy (e.g., hydroxyurea), immunomodulatory drug therapy (e.g., thalidomide), immunosuppressive therapy, corticosteroids \> 10 mg/day prednisone or equivalent, or growth factor treatment (e.g., erythropoietin) within 14 days prior to initiation of study drug. * Incomplete recovery from major surgery within four weeks of study entry. * Radiation therapy within four weeks of study entry. * Women of childbearing potential, unless surgically sterile for at least 3 months (i.e., hysterectomy), OR postmenopausal for at least 12 months (FSH \> 30 U/mL), OR unless they 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. * Men who partner with a woman of childbearing potential, unless they agree to take appropriate precautions to avoid pregnancy (with at least 99% certainty) from screening through to the end of study. Permitted methods for preventing pregnancy must be communicated to study subjects and their understanding confirmed. * Females who are pregnant or are currently breastfeeding. * Known positive status for HIV. * Clinically active hepatitis B or C. * Diagnosis of another malignancy unless free of disease for at least three years following therapy with curative intent. Patients with early-stage basal cell or squamous cell skin cancer, cervical intraepithelial neoplasia, cervical carcinoma in situ or superficial bladder cancer may be eligible to participate at the Investigator's discretion. * Any acute active infection. * Cardiac dysrhythmias requiring treatment, or prolongation of the QTc (Fridericia) interval to \>450 msec for males or \>470 msec for females at pre-study screening, unless attributable to pre-existing bundle branch block. * Presence of \>= Grade 2 peripheral neuropathy. * Uncontrolled congestive heart failure (New York Heart Association Classification 3 or 4), uncontrolled or unstable angina, myocardial infarction, cerebrovascular accident, or pulmonary embolism within 3 months prior to initiation of study drug. * Uncontrolled inter current illness or any concurrent condition that, in the Investigator's opinion, would jeopardize the safety of the patient or compliance with the protocol.