Open Label Study to Evaluate the Activity of Imetelstat in Patients With Essential Thrombocythemia or Polycythemia Vera

For patients with ET: To obtain a preliminary estimate of efficacy of imetelstat, as measured by best hematologic response within the first year of therapy in patients with ET who have failed or are intolerant to at least one prior therapy, or who have refused standard therapy. For patients with PV: To obtain a preliminary estimate of efficacy of imetelstat, as measured by maintenance of Hct \< 45% in men and \< 42% in women (or pre-specified Hct count that is tolerable) without phlebotomy or myelosuppressive therapy within the first year of therapy in patients with PV who have failed or are intolerant to at least one prior therapy, or who have refused standard therapy.