Immunogenicity of panitumumab in combination chemotherapy clinical trials

Three validated assays (two screening immunoassays and a neutralizing antibody bioassay) were used to detect the presence of anti-panitumumab antibodies in serum samples collected from patients enrolled in four panitumumab combination chemotherapy clinical trials. The impact of anti-panitumumab antibodies on pharmacokinetic and safety profiles was analyzed using population pharmacokinetic analysis and descriptive statistics, respectively.Of 1124 patients treated with panitumumab in combination with oxaliplatin- or irinotecan-based chemotherapy with postbaseline samples available for testing, 20 (1.8%) patients developed binding antibodies and 2 (0.2%) developed neutralizing antibodies. The incidence of anti-panitumumab antibodies was similar in patients with tumors expressing wild-type or mutant KRAS and in patients receiving oxaliplatin- or irinotecan-based chemotherapies. No evidence of an altered pharmacokinetic or safety profile was found in patients who tested positive for anti-panitumumab antibodies.The immunogenicity of panitumumab in the combination chemotherapy setting was infrequent and similar to the immunogenicity observed in the monotherapy setting. Panitumumab immunogenicity did not appear to alter pharmacokinetic or safety profiles. This low rate of immunogenicity may be attributed to the fully human nature of panitumumab.ClinicalTrials.gov: NCT00339183 (study 20050181), NCT00411450 (study 20060277), NCT00332163 (study 20050184), and NCT00364013 (study 20050203).Panitumumab is a high affinity (Kd = 5 × 1011 M) fully human IgG2 monoclonal antibody (mAb) directed against human epidermal growth factor receptor (EGFR). Panitumumab is indicated as monotherapy for the treatment of metastatic colorectal cancer (mCRC) after disease progression on fluoropyrimidine, oxaliplatin, and irinotecan chemotherapy regimens in the United States (US) and European Union (EU) [1,2]. In the US, treatment of patients whose tumors have KRAS mutations in codon 12 or 13 is not