Erbitux (cetuximab) is a monoclonal antibody to EGFR, and it's actually made from a protein that is part mouse and part human (called a chimeric protein, named for the mythologic creature chimera that was composed of multiple parts from different animals). It's uncommon but not rare for patients to have an allergic reaction to this protein, and in most large national and international studies show rates of hypersensitivity reactions (HSRs) in the 1-3% range.