A phase 2 clinical trial of panitumumab monotherapy in Japanese patients with metastatic colorectal cancer

Objective: Panitumumab, a fully human monoclonal antibody targeting epidermal growth factor receptor (EGFR), has antitumor activity and an acceptable safety profile in patients with metastatic colorectal cancer (mCRC). This Phase 2 study evaluated efficacy, pharmacokinetics and safety of panitumumab in Japanese patients with mCRC who developed progressive disease during or after fluoropyrimidine, irinotecan and oxaliplatin chemotherapy. Methods: Eligible patients had histologically proven colorectal adenocarcinoma and EGFR tumor expression in ≥1% of tumor cells by immunohistochemistry. Patients received panitumumab 6 mg/kg every 2 weeks until disease progression or unacceptable toxicity. The primary endpoint was objective response rate (ORR) per modified Response Evaluation Criteria in Solid Tumors (RECIST) by independent central review. Secondary endpoints included progression-free survival (PFS), overall survival (OS), pharmacokinetic parameters and incidence of adverse events. Results: Fifty-two patients received at least one dose of panitumumab. Seven patients had partial responses for a confirmed ORR of 13.5% (95% CI: 5.6, 25.8). Median PFS was 8.0 weeks (95% CI: 7.4, 11.4) and median OS was 9.3 months (95% CI: 7.1, 12.8). Panitumumab pharmacokinetics were consistent with prior studies in Japanese and non-Japanese patients. The most common treatment-related adverse events (all, worst grade 3) were acne (81%, 2%), dry skin (62%, 0%), rash (46%, 2%), paronychia (33%, 2%), pruritus (33%, 0%) and hypomagnesemia (33%, 0%). No adverse event of infusion reaction was reported by the investigators. Conclusions: Panitumumab monotherapy was active in Japanese patients with chemotherapy-refractory mCRC, with pharmacokinetic and safety profiles similar to those seen in prior studies.