Updated Interim Long-Term Follow-up Data Reported AMG 531 Dosed Once Weekly Increased and Sustained Platelet Counts in Patients with Immune Platelet Disorder.

ORLANDO, Fla. -- Amgen (NASDAQ: AMGN) today announced interim results from an open-label extension study showing that long-term administration (up to 48 weeks) of its investigational therapy AMG 531 stimulated platelet production and was generally well-tolerated in adult patients with immune thrombocytopenic purpura (ITP). These updated interim data were presented in an oral session at the American Society of Hematology (ASH) 48th Annual Meeting in Orlando, Fla. (Abstract # 476)

ITP is a chronic and potentially serious bleeding disorder caused by an immune system malfunction that mistakenly recognizes the body's own platelets as foreign and destroys them, as well as a decrease in platelet production, which results in low platelet counts. Platelets are specialized blood cells that help prevent and stop bleeding by participating in clotting. The risk of a bleeding event increases when platelet counts drop to less than 30,000 platelets per microliter.

"Unlike most current ITP treatments, which interfere with platelet destruction, AMG 531 is designed to increase the production of platelets at a rate that outpaces their destruction by the immune system," said David J. Kuter, M.D., D.Phil., director of Center for Hematology, Massachusetts General Hospital, Boston. "This study now includes two years of follow-up data and the interim results at 48 weeks are encouraging. Individualized dosing of AMG 531 may provide a new option for patients with ITP, potentially allowing tapering off of steroid therapy."

The long-term follow-up study has been ongoing for more than two years and is open to patients who have completed a previous AMG 531 study. To date, 104 patients have been enrolled. This planned interim analysis at 48 weeks includes 36 patients, who previously completed a Phase 2 trial, with AMG 531. Overall, 86 percent of patients (n=31) achieved a platelet response, defined as achieving platelet count of at least 50,000 platelets per microliter of blood and doubling of their baseline. At 48 weeks, more than 57 percent of patients still on study (n=23) had maintained this platelet response. The median time to first response was three weeks and the mean dose at first response was 3.4 og/kg.

Thirty patients had undergone splenectomy prior to study enrollment and nine were receiving concurrent corticosteroids, which were able to be tapered when platelet counts reached greater than 50,000 platelets per microliter of blood. Of the nine patients on concurrent corticosteroids, 67 percent (n=6) discontinued corticosteroid treatment and 11 percent (n=1) had at least a 25 percent corticosteroid dose reduction.

In this study, AMG 531 appeared generally well-tolerated. The most frequently reported adverse events were headache, upper respiratory infection and fatigue. Four patients experienced serious treatment-related adverse events, including bone pain, vaginal hemorrhage/anemia, transverse sinus thrombosis, and reversible increased bone marrow reticulin (reported as myelofibrosis). No neutralizing antibodies have been detected to date.

About the Study

This ongoing, open-label extension study is assessing the safety and efficacy of long-term administration of AMG 531 in both pre- and post-splenectomy ITP patients. Eligible patients have completed a previous AMG 531 study in ITP, including those from two recent Phase 3 AMG 531 studies in ITP, and have a baseline platelet count of less than 50,000 platelets per microliter, with no recent significant change in medical history. The AMG 531 starting dose was 1 og/kg by subcutaneous injection with dose adjustment to a maximum of 15 og/kg. Patients were administered AMG 531 by injection once weekly unless their platelet count exceeded 400,000 platelets per microliter. Concurrent corticosteroid treatment could be tapered when patients' platelet counts reached 50,000 platelets per microliter. Data for patients previously enrolled in the Phase 3 trials are still blinded.

For further information on AMG 531 clinical trials, please visit www.amgentrials.com.

About AMG 531

AMG 531 is an investigational thrombopoiesis-stimulating protein ("peptibody") that contains two component regions. Peptibodies are engineered therapeutic molecules that can bind to human drug targets and contain peptides linked to the constant domains of antibodies. AMG 531 works similarly to thrombopoietin (TPO), a natural protein in the body. The active peptide component stimulates the TPO receptor, which is necessary for growth and maturation of bone marrow cells and plays a very important role in platelet production. In 2004, the U.S. Food and Drug Administration (FDA) granted fast track designation for AMG 531. Orphan designation for ITP was granted in 2003 by the FDA and in 2005 by the European Agency for the Evaluation of Medicinal Products (EMEA).

About ITP

Immune (idiopathic) thrombocytopenic purpura (ITP) is a chronic and potentially serious autoimmune bleeding disorder characterized by low levels of platelets in the blood, a condition known as thrombocytopenia. A normal platelet range for a person without ITP is 150,000 - 400,000 platelets per microliter of blood. The risk of a bleeding event increases when platelet counts drop to less than 30,000 platelets per microliter.

With ITP, platelets are destroyed by the patient's own immune system. ITP has historically been considered a disease of platelet destruction; however, recent data also suggest that the body's natural platelet production processes are unable to compensate for low levels of platelets in the blood. Increasing the rate of platelet production may address low platelet levels associated with ITP.

According to the Platelet Disorder Support Association, approximately 200,000 Americans have been diagnosed with ITP. Additionally, in the United States and Europe combined, ITP is estimated to affect 50 to 100 new persons per million annually.

About Amgen

Amgen discovers, develops and delivers innovative human therapeutics. A biotechnology pioneer since 1980, Amgen was one of the first companies to realize the new science's promise by bringing safe and effective medicines from lab, to manufacturing plant, to patient. Amgen therapeutics have changed the practice of medicine, helping millions of people around the world in the fight against cancer, kidney disease, rheumatoid arthritis, and other serious illnesses. With a deep and broad pipeline of potential new medicines, Amgen remains committed to advancing science to dramatically improve people's lives. To learn more about our pioneering science and our vital medicines, visit www.amgen.com.

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