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DNA Test Predicts Harmful Effects of Cancer Drug
Study Questions FDA Guidelines for Colon Cancer Drug
CHAPEL HILL, N.C., Aug. 28 /PRNewswire/ -- Not everyone needs a genetictest before taking the cancer drug irinotecan, and the U.S. Food and DrugAdministration should modify its prescription guidelines to say so, accordingto researchers at the University of North Carolina at Chapel Hill.
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Irinotecan, also known by its brand name Camptosar, is used mainly as asecond-line treatment for colorectal cancer, the third most common form ofcancer in the United States. The FDA currently recommends screening patientsfor a gene that could make them more susceptible to the harmful side effectsof the drug, the most worrisome of which is neutropenia, a blood disordercharacterized by an abnormally low number of white blood cells, whichdecreases the body's ability to fight off infections.
In a paper published in the September 5 Journal of the National CancerInstitute, UNC's Dr. Janelle Hoskins (PhD) and colleagues analyzed data fromnine previous studies of irinotecan. They found that only patients whoreceived a medium or high dose of the drug had greater risk of neutropenia ifthey had two copies of a variation of the gene UGT1A1, known as UGT1A1*28. Atlower doses, however, the risk was the same regardless of what UGT1A1 gene thepatients had.
"Many institutions saw the FDA's recommendation as authorization to testall patients before treating them with irinotecan, even though many cliniciansdidn't think it was always necessary since low doses of the drug weren'tcausing problems," said Prof. Howard McLeod, senior author of the study anddirector of the UNC Institute for Pharmacogenomics and Individualized Therapy.
"Our review showed that at low doses, the drug is well tolerated and canbe taken by most people," McLeod said. "Testing only becomes essential whenthe dosage increases and genetics become a larger factor in determining whatside effects patients experience".
Having a genetic test available for a medicine is valuable, but so isknowing when to use that test, said Dr. Richard Goldberg, a co-author of thestudy and physician in chief of the Carolina Cancer Hospital.
"There are so many treatment options for cancer patients that the moreinformation we have about matching the right therapy to the patient, thebetter off we all are," Goldberg said. "Studies like this one give oncologiststhe tools needed to take better care of patients while avoiding unnecessarytests and expenses."
The authors recommended that the FDA amend the product information foririnotecan to describe the association between irinotecan dose and risk ofhematologic toxicity among patients with two UGT1A1*28 genes.
About the authors:
McLeod is the Fred Eshelman Distinguished Professor at the UNC School ofPharmacy. Goldberg is the associate director of UNC's Lineberger ComprehensiveCancer Center and chief of the UNC Division of Hematology/Oncology. Hoskins isof the UNC School of Pharmacy. Qu and Ibrahim are of the UNC School of PublicHealth.
For more information about this study, please contact Professor HowardMcLeod, Director, UNC Institute for Pharmacogenomics and IndividualizedTherapy, University of North Carolina at Chapel Hill by phone at 919-966-0512or 314-420-8182, or b
