Interim results were presented for 34 patients treated with AMG 531 for up to 48 weeks. Twenty-eight patients had undergone splenectomy before study entry and eight were receiving concurrent corticosteroids for ITP. Overall, 47 percent of patients (n=16) had a durable platelet response, defined as platelet response at six or more weeks between weeks 18 through 25. Of the eight patients on concurrent corticosteroids, 50 percent (n=4) discontinued corticosteroid treatment and 25 percent (n=2) had at least a 50 percent dose reduction.

"It is exciting that most patients in this study achieved platelet counts of greater than 50,000 per microliter, despite how refractory they were, from a starting count of approximately 18,000," said James B. Bussel, M.D., professor of pediatrics and medicine at the Weill Cornell Medical Center, New York, NY. "This is important because it suggests that AMG 531 may stimulate platelet production faster than the immune system can destroy them, enabling patients to sustain a satisfactory platelet count with ongoing AMG 531 treatment."

In this study, AMG 531 was generally well-tolerated. The most frequently reported adverse events were headache, upper respiratory infection and fatigue. Serious adverse events reported as treatment related include bone pain (n=1); anemia (n=1); and vaginal hemorrhage (n=1). Additionally, there was one reported case of diffuse reticulin formation in the bone marrow reported as myelofibrosis. Reticulin formation is hypothesized as due to excessive accumulation of megakaryocytes in the bone marrow. Follow-up bone marrow biopsies reveal that the reticulin is improving. 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 a
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Contact: Trish Hawkins
805-447-4587
Porter Novelli
12-Dec-2005