Updated results from a dose and schedule study of Panitumumab (ABX-EGF) monotherapy, in patients with advanced solid malignancies

Abstract

3059 Background: Panitumumab is a fully human monoclonal antibody to the epidermal growth factor receptor (EGFr). This open-label, multiple-infusion, dose-escalation trial evaluated the safety, pharmacokinetics (PK), and antitumor activity of panitumumab in advanced solid tumor patients. Methods: Sequential cohorts of patients were enrolled to receive four infusions at different dose levels and schedules of panitumumab monotherapy ranging from 0.01 to 5.0 mg/kg once per week (QW), 6.0 mg/kg once every 2 weeks (Q2W) or 9.0 mg/kg once every 3 weeks (Q3W) administered IV over one hour without premedication. Patients were prescreened for EGFr expression and had to have at least 1+ expression in ≥10% of tumor cells. Stable or responding patients were eligible for extended panitumumab treatment on a separate protocol for six additional months or until disease progression. Patients had to have acceptable organ function, and may have received prior systemic anti-tumor therapy. Preliminary results are presented below. Results: Ninety-six patients (72 [75%] men) were treated with panitumumab. The mean age was 60.4 yrs (range 32–79). Tumor types included 39 colorectal (CRC), 14 lung, 3 pancreatic, 21 prostate, 15 renal, 3 esophageal/gastrosophageal, and 1 anal cancer. The incidence of skin-related toxicities was dose dependent and plateaued at >2.0 mg/kg QW. Grade 3 or 4 related adverse events were noted in 10% of patients with grade 3 skin-related toxicities being the most frequent (7% of patients). No MTD was reached. No human anti-human antibody formation or infusion related reactions were observed. PK exposure was similar between 2.5 mg/kg QW, 6 mg/kg Q2W and 9 mg/kg Q3W. By investigator assessment, 5 confirmed partial responses (WHO) (12.8% RR, 5/39 CRC patients), 1 minor PSA response, and 18 patients with stable disease were observed. Conclusions: Panitumumab is generally well tolerated. The exposure and tolerability profile is comparable between QW, Q2W, and Q3W schedules. Panitumumab has single agent anti-tumor activity in solid tumors, most notably in subjects with advanced CRC. Author Disclosure Employment or Leadership Consultant or Advisory Role Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration Abgenix, Amgen