Study finds immune system can cause reaction to cancer drug

By Maggie Fox, Health and Science Editor

WASHINGTON (Reuters) - People who live in parts of the U.S. south may have pre-existing immunities that cause a severe allergic reaction to the cancer drug Erbitux, U.S. researchers reported on Thursday.

They found that patients who had sometimes life-threatening reactions had a pre-existing immunity to a sugar compound found in the drug made by ImClone Systems Inc..

The discovery, reported in the New England Journal of Medicine, might help explain why people living in certain regions of the United States are more likely to have the reaction, the researchers said.

And because the drug is so widely used -- it had global sales of $1.1 billion in 2006 for use in treating colon, head and neck cancers -- potential patients should be tested first, the researchers said.

Erbitux, known generically as cetuximab, is a monoclonal antibody, a genetically engineered immune system compound designed to home in specifically on cancer cells.

But some patients have a severe allergic reaction to the drug.

Dr. Thomas Platts-Mills of the University of Virginia and colleagues looked at reports of these cases, which suggest that as many as 22 percent of patients treated with Erbitux in Tennessee and North Carolina reported some kind of reaction, including anaphylaxis, which can rapidly lead to difficulty breathing, shock or fainting.

"It's stunning," Platts-Mills said in a telephone interview.