The KRAS RGQ PCR kit checks for the presence of a certain mutation in the KRAS gene. About 40 percent of people with colon cancer are thought to have the mutation, which renders Erbitux ineffective. The test is for people whose colorectal cancer has spread to other parts of the body, the FDA said in a news release.

The American Cancer Society says more than 141,000 new cases of colon cancer were diagnosed last year in the United States, and nearly 50,000 people died of the disease.

Erbitux (cetuximab), co-marketed by Bristol-Myers Squibb and Eli Lilly, was first approved as a colon cancer treatment in 2004.

The new diagnostic was developed by Qiagen Manchester Ltd., based in Manchester, England.

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