Additional Study Information: The purpose of the study is to evaluate the efficacy and safety of imetelstat for the treatment of patients with myelodysplastic syndrome (MDS). All patients participating in Part 1 of this study will get 7.5 mg/kg of imetelstat as a 2-hour intravenous infusion once every 4 weeks. The dose of imetelstat may be increased, held or decreased depending on how well imetelstat works to treat your MDS and whether or not you have certain side effects to treatment. Before receiving imetelstat, you will receive 25-50mg of diphenhydramine (an antihistamine) and 100-200 mg of hydrocortisone (a corticosteroid), or equivalent.