And no one knows why. The med - which is used to treat colon cancer and head and neck tumors - is being studied for treating ovarian, lung, breast and gastrointestinal tumors at various sites in the Southeast US. And that’s where researchers noticed an unusually high rate of allergic reaction in cancer patients, according to the Journal of Clinical Oncology (subscription required).

When Erbitux was first approved, the first three patients treated as part of a study conducted at the University of North Carolina had severe reactions to the drug. Docs at two sites in Nashville also had more patients than expected react with a drop in blood pressure and shortness of breath or other hypersensitivity reactions within minutes of infusion, according to a UNC statement.

The patients were clustered along a line stretching across North Carolina, Tennessee, northern Arkansas and southern Missouri, according to study leader Bert O’Neil, assistant professor of medicine, at UNC’s division of hematology and oncology. So they reviewed more than 140 patients from ongoing clinical trials and current clinical records.

The nationwide rate of severe allergic reactions to Erbitux is about 2 percent. However, 22 percent of patients in this study had severe allergic reactions. Erbitux normally is infused over a two-hour period, but allergic patients had a reaction within minutes of infusion, a classic anaphylactic reaction. The strongest predictor of a reaction was a history of other hypersensitivities, such as allergic asthma, food allergies, bee stings or allergies to other drugs, such as penicillin, according to UNC.

Meanwhile, UNC says Bristol-Myers Squibb, which markets the ImClone Systems drug, is studying a screening test. For now, though, this places a new limitation on Erbitux use, certainly in that part of the country.