Poordad, F.

261 Background: Mapatumumab is a fully human agonist monoclonal antibody to the tumor necrosis factor-related apoptosis-inducing ligand receptor 1 (TRAIL-R1). Sorafenib targets Mcl-1, a key TRAIL resistance protein, and accordingly could enhance mapatumumab's pro-apoptotic activity. Based on this and on preclinical data on mapatumumab in HCC cell lines, the current dose-escalation study is evaluating mapatumumab in combination with sorafenib in patients with advanced HCC. Methods: Eligible patients had advanced HCC, Child-Pugh A or Model for End-Stage Liver Disease score < 15, and were positive for hepatitis B surface antigen or hepatitis C antibody. Intravenous mapatumumab was administered at 3, 10 or 30 mg/kg every 21 days with sorafenib (400 mg twice daily) until disease progression or unacceptable toxicity. Dose-limiting toxicities (DLTs) included events considered at least possibly related to mapatumumab and/or its interaction with sorafenib. Tumor measurements were performed every 2 cycles. Dose escalation required at least 3 patients in a cohort to receive >= 50% of full-dose sorafenib in the first 2 cycles. Results: To date, 19 patients have been enrolled in the 3 mg/kg (n=6), 10 mg/kg (n=9) and 30 mg/kg (n=4) cohorts and have received a median of 4 cycles (range 1 to 24 cycles); 4 patients have received >= 11 cycles. The maximum tolerated dose has not been reached. DLTs that prompted expansion of the 3 mg/kg and 10 mg/kg cohorts were elevations of amylase and/or lipase (1 at 3 mg/kg, 1 at 10 mg/kg). Other Grade 3-4 events considered at least possibly related to mapatumumab and/or its interaction with sorafenib included hepatic pain (1/17), thrombocytopenia (1/17), increased aspartate aminotransferase (1/17), increased lipase (1/17), and increased gamma-glutamyltransferase (1/17). Two patients have had a partial response and 4 patients have had stable disease lasting > 12 weeks, based on investigator assessment. Conclusions: Mapatumumab was well-tolerated at doses up to 30 mg/kg in combination with sorafenib in patients with HCC and viral hepatitis. A randomized phase II study of this combination in patients with advanced HCC is planned. [Table: see text]