Purpose: Monoclonal antibodies against the epidermal growth factor receptor approved for treating metastatic colorectal cancer (mCRC) include cetuximab (a chimeric antibody) and panitumumab (a fully human antibody). Because these antibodies have differences in protein sequence, patients intolerant to one antibody might still tolerate the other. Four cases are presented from a US panitumumab compassionate-use program in which patients with mCRC who were intolerant to cetuximab received panitumumab.
Patients and methods: Eligible patients had failed previous fluoropyrimidine therapy with oxaliplatin- and irinotecan-containing chemotherapy, had cetuximab intolerance (ie, experienced an infusion reaction), and were unable to participate in a panitumumab clinical trial. For each patient, individual Federal Drug Administration-approved single-patient treatment use Investigational New Drug- and Institutional Review Board-approved protocols were used, informed consent was obtained, and data were collected independently by the investigator.
Results: All 4 patients (2 men, 2 women) had received previous bevacizumab and premedications before cetuximab administration. In response to cetuximab, all 4 patients experienced Common Terminology Criteria for Adverse Events grade 3 or grade 4 infusion-reaction symptoms, which required acute therapy. Time from cetuximab discontinuation to panitumumab administration ranged from 8 days to 5 months. Panitumumab monotherapy was administered at approximately 6 mg/kg every 2 weeks. Two patients received premedications before panitumumab use. No physician reported any infusion reaction to panitumumab. One patient had stable disease, and 3 patients had disease progression.
Conclusion: Though this small case series provides evidence that patients with mCRC intolerant to cetuximab can receive subsequent panitumumab monotherapy without experiencing infusion reactions, additional clinical testing is needed to definitively examine this finding.