P3 Study to Evaluate Efficacy and Safety of AMG 531 in Thrombocytopenic Japanese Subjects With Immune (Idiopathic) Thrombocytopenic Purpura

Inclusion Criteria:

• Japanese patients with diagnosis of ITP according to the diagnostic criteria proposedby Research Committee for Idiopathic Hematopoietic Disorders of the Ministry ofHealth, Labour and Welfare [MHLW] (revised in 1990) at least 6 months before the firstscreening visit
• The mean of the 3 scheduled platelet counts taken at the scheduled visits during thescreening period must be ≤ 30 x 10^9/L, with no individual count > 35 x 10^9/L
• Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 2
• Subjects must be ≥ 20 years of age at the time of obtaining the informed consent
• Have received at least 1 prior treatment for ITP
• If known Helicobacter pylori positive, having completed one course of Helicobacterpylori eradication therapy at least 12 weeks before the first screening visit
• A hemoglobin value taken at scheduled visit during the screening period must be ≥ 10g/dL
• A serum creatinine concentration taken at scheduled visit during the screening periodmust be ≤ 2 mg/dL
• Adequate liver function, as evidenced by a total bilirubin taken at scheduled visitduring the screening period ≤ 1.5 times of the upper limit of the normal range (exceptfor patients with a confirmed diagnosis of Gilbert's Disease) or an alanineaminotransferase and aspartate aminotransferase taken at the screening visit ≤ 3 timesof the upper limit of the normal range

Exclusion Criteria:

• Any known history of bone marrow stem cell disorder. Any abnormal bone marrow findingsother than those typical of ITP.
• Any active malignancy. If prior history of cancer other than basal cell carcinoma orcervical carcinoma in situ, no treatment or active disease within 5 years before thefirst screening visit.
• Documented diagnosis of arterial thrombosis (eg, stroke, transient ischemic attack, ormyocardial infarction); history of venous thrombosis (eg, deep vein thrombosis,pulmonary embolism) and receiving anticoagulation therapy at the first screeningvisit.
• Documented diagnosis of anti phospholipid antibody syndrome
• Currently receiving any treatment for ITP except oral corticosteroids, azathioprineand/or danazol administered at a constant dose and schedule from at least 4 weeksprior to the first screening visit
• Received intravenous immunoglobulin, anti D immunoglobulin, or any drug administeredto increase platelet counts (eg, immunosuppressants except azathioprine) within 2weeks before the first screening visit
• Have had a splenectomy for any reason within 12 weeks before the first screening visit
• Past or present participation in any study evaluating pegacaristim (polyethyleneglycol-conjugated recombinant human megakaryocyte growth and development factor,KRN9000), Eltrombopag (SB 497115), recombinant human thrombopoietin, AMG 531, or otherMpl stimulation product
• Received hematopoietic growth factors (eg, granulocyte colony stimulating factor,macrophage colony stimulating factor, erythropoietin, interleukin 11) for any reasonwithin 4 weeks before the first screening visit
• Received any anti malignancy agents (eg, cyclophosphamide, 6 mercaptopurine,vincristine, vinblastine, Interferon alfa) for any reason within 8 weeks before thefirst screening visit
• Received any monoclonal antibody drugs (eg, rituximab) for any reason within 14 weeksbefore the first screening visit
• Less than 4 weeks since receipt of any therapeutic drug or device that is not MHLWapproved for any indication before the first screening visit
• Pregnant or breast feeding
• Subjects of reproductive potential who are not using adequate contraceptiveprecautions, in the judgment of the investigator
• Known severe drug hypersensitivity
• Concerns for subject's compliance with the protocol