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Dose and Schedule Study of Panitumumab Monotherapy in Patients with Advanced Solid Malignancies

Authors' Affiliations: ¹ Georgetown University Medical Center, Washington, District of Columbia; ² University of California at Los Angeles School of Medicine, Los Angeles, California; ³ Duke University Medical Center, Durham, North Carolina; ⁴ Cancer Therapy and Research Center, San Antonio, Texas; ⁵ Abgenix, Inc., Fremont, California; and ⁶ Amgen, Inc., Thousand Oaks, California

Requests for reprints: Louis M. Weiner, Georgetown University Medical Center Research Building, Suite E501, 3970 Reservoir Road Northwest, Washington DC 20057-1465. Phone: 202-687-2110; Fax: 202-687-6402; E-mail: Weinerl{at}georgetown.edu.

Purpose: This phase 1 study evaluated the safety, pharmacokinetics, and activity of panitumumab, a fully human, IgG2 monoclonal antibody that targets the epidermal growth factor receptor in patients with previously treated epidermal growth factor receptor–expressing advanced solid tumors.

Experimental Design: Sequential cohorts were enrolled to receive four i.v. infusions of panitumumab monotherapy at various doses and schedules. Safety was continuously monitored. Serum samples for pharmacokinetic, immunogenicity, and chemistry assessments were drawn at preset intervals. Tumor response was assessed at week 8.

Results: Ninety-six patients received panitumumab. Median (range) age was 61 years (32-79 years), and 72 (75%) patients were male. Tumor types were 41% colorectal cancer, 22% prostate, 16% renal, 15% non–small cell lung, 3% pancreatic, 3% esophageal/gastroesophageal, and 1% anal. The overall incidence of grade 3 or 4 adverse events was 32% and 7%, respectively. The incidence of skin-related toxicities was dose dependent. No maximum tolerated dose was reached. No human anti-panitumumab antibodies were detected. No investigator-determined panitumumab infusion-related reactions were reported. Serum panitumumab concentrations were similar in the 2.5 mg/kg weekly, 6.0 mg/kg every 2 weeks, and 9.0 mg/kg every 3 weeks dose cohorts. Five of 39 patients (13%) with colorectal cancer had a confirmed partial response, and 9 of 39 patients (23%) with colorectal cancer had stable disease.

Conclusions: Panitumumab was well tolerated with comparable exposure and safety profiles for the weekly, every 2 weeks, and every 3 weeks administration schedules. Rash and dry skin occurred more frequently in the dose cohorts receiving 2.5 mg/kg weekly dose. Panitumumab has single-agent antitumor activity, most notably in patients with advanced colorectal cancer.