Safety and efficacy of panitumumab following cetuximab: retrospective review of the Memorial Sloan-Kettering experience.

There are two highly selective antibodies to the epidermal growth factor receptor (EGFR) now available for use in metastatic colorectal cancer (mCRC). In KRAS wild type patients, cetuximab (Cmab)-an IgG1 chimeric molecule--has activity alone and in combination with chemotherapy for the first, second and third-line settings. Panitumumab (Pmab)--a fully humanized IgG2 molecule--has activity as a single agent in chemorefractory mCRC and shows promising activity in combination with chemotherapy. It remains unclear which antibody to use. This retrospective review of our experience with Pmab in 13 EGFR antibody-naive patients and in 22 patients previously treated with Cmab for mCRC highlights a lack of hypersensitivity reactions (HSR) with Pmab, even in patients who experienced HSR to Cmab. In patients who received Cmab, 22% developed grade 3-4 HSR. There were no HSR on subsequent treatment with Pmab. We demonstrate similar activity in 95% of cases, between Cmab and Pmab both alone and in combination with chemotherapy in the treatment of mCRC. In one case we report unique sensitivity to Pmab after progression with Cmab.