My Cancer Advisor > Colon and Rectal Cancer > Experiencing Chemotherapy for Colon and Rectal Cancer > Genetic Test for Avoiding Toxicity from a Colon Cancer Drug

Genetic Test for Avoiding Toxicity from a Colon Cancer Drug

Everyone responds to different medicines for cancer: how it is absorbed in the intestinal tract, how it is metabolizes (broken down or altered) in the liver and other organs, and how it is excreted from the body. This short FDA video on genetic testing explains how a new genetic test can help identify those who may have more severe reactions to the toxic effects of a popular drug called Camptosar.

According to the FDA report, a gene called UGT1A1 produces an enzyme that metabolizes Camptosar. Variations in this gene can influence a patient’s ability to break down the drug. About 10 percent of the North American population has a variation of the UGT1A1 gene that reduces their ability to metabolize Camptosar, leading to high blood levels of the drug and a higher risk of toxic side effects. If these patients are given standard doses of Camptosar, about half will develop severe neutropenia, which can be fatal.

A test, called the Invader UGT1A1 Molecular Assay, can identify whether a patient has the genetic variant affecting the metabolism of Camptosar and thus would be at higher risk for developing severe neutropenia. The drug label says to consider lowering the starting dose of the Camptosar for those patients found to be high risk.

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