Clinicians have been perplexed by the fact that some patients given the drug cetuximab (Erbitux®)–an immune-based therapy commonly used to treat persons diagnosed with head and neck cancer, or colon cancer–have a severe and rapid adverse reaction to the drug. Sometimes the reaction includes anaphylaxis, a life-threatening condition characterized by a drop in blood pressure, fainting, difficulty breathing, and wheezing. The drug is currently being tested in patients with non-small cell lung cancer.