Determination of Safe Dose of Romiplostim (AMG 531) in Patients With Myelodysplastic Syndromes (MDS)

Inclusion Criteria: * Diagnosis of MDS using the World Health Organization classification * Low or Intermediate-1 risk MDS using the International Prognostic Scoring System (IPSS) * The mean of two platelet counts taken during the screening period must be ≤ 50 x 10\^9/L, with no individual count \> 55 x 10\^9/L (The mean platelet counts of 5 subjects enrolled at the maximum tolerated dose (MTD) must be ≤ 20 x 10\^9/L). Standard of care platelet assessments taken prior to Informed Consent may be used as 1 of the 2 counts taken within 3 weeks prior to study day 1. * Must be ≥ 18 years of age at the time of obtaining informed consent * Eastern Cooperative Oncology Group (ECOG) performance status of 0-2 at the time of screening * Adequate Liver Function, as evidenced by a serum bilirubin ≤ 1.5 times the laboratory normal range (except for patients with a confirmed diagnosis of Gilbert's Disease), alanine aminotransferase (ALT) ≤ 3 times the laboratory normal range, and aspartate aminotransferase (AST) ≤ 3 times the laboratory normal range * A serum creatinine concentration ≤ 2 mg/dL (≤ 176.6 µmol/L) * Before any study-specific procedure, the appropriate written informed consent must be obtained (see Section 12.1) Exclusion Criteria: * Currently receiving any treatment for MDS other than transfusions and erythropoietic growth factors. If granulocyte growth factors are currently being received, they cannot be used on or after study day 1 * Clinically significant bleeding within 2 weeks prior to screening (eg, gastrointestinal (GI) bleeds, intracranial hemorrhage) * Prior malignancy (other than controlled prostate cancer, in situ cervical cancer or basal cell cancer of the skin) unless treated with curative intent and without evidence of disease for ≥ 3 years before screening * Prior history of bone marrow transplantation * Persistent peripheral blood monocytosis (≥ 3 months with an absolute monocyte count \> 1,000/µL) * Unstable angina, congestive heart failure (New York Heart Association \[NYHA\] \> class II), uncontrolled hypertension (diastolic \> 100 mmHg), uncontrolled cardiac arrhythmia, or recent (within 1 year) myocardial infarction * Received Anti-Thymocyte Globuline (ATG) within 6 months of screening * Received hypomethylating agents, immunomodulating agents, histone deacetylase inhibitors, cyclosporine or mycophenolate within 6 weeks of screening * Received interleukin (IL)-11 (oprelvekin) within 4 weeks before screening * Concurrent use of granulocyte growth factors (i.e. granulocyte-colony stimulating factor \[G-CSF; Neupogen, Granocyte\], pegfilgrastim \[Neulasta\], granulocyte macrophage-colony stimulating factor \[GM-CSF; Leukine, Prokine, Sargramostim\]) * Have ever previously received recombinant thrombopoietin (rTPO), pegylated recombinant human megakaryocyte growth and development factor (PEG-rHuMGDF), eltrombopag, or romiplostim * Less than 4 weeks since receipt of any therapeutic drug or device that is not Food and Drug Administration (FDA) approved for any indication * Other investigational procedures are excluded * History of arterial thrombosis (eg, stroke or transient ischemic attack) in the past year * History of venous thrombosis that currently requires anti-coagulation therapy * Untreated B12 or folate deficiency * Subject is evidently pregnant (eg, positive human chorionic gonadotropin \[HCG\] test) or is breast feeding * Subject is not using adequate contraceptive precautions * Subject has known hypersensitivity to any recombinant E coli-derived product * Subject previously has enrolled in this study * Subject will not be available for follow-up assessment * Subject has any kind of disorder that compromises the ability of the subject to give written informed consent and/or to comply with study procedures