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Genetic test problems.

Some breast cancer drugs target certain types of cancer cells. Herceptin, for example, is designed to destroy cancer cells that possess too much Her-2 protein. Other drugs, like Tamoxifen and Faslodex, inhibit cancer growth by competing with hormone receptors found on some types of cancer cells. Doctors use two laboratory tests to determine which, if any, of these targeted drugs would benefit a patient. Unfortunately, the tests are unreliable, according to a Wall Street journal article (January 4, 2008).

Target-drug tests involve subjective evaluations of the cancer tissue by a pathologist. Experience with the tests seems to be the biggest factor in accuracy, but laboratory protocols are also an issue. For example, if the tissue has been stored in a refrigerator or in a preservative over a weekend, the results are less likely to be accurate. A 2006 study of Her-2 tests performed in several US laboratories found that 14% to 16% of the positive Her-2 tests were wrong. That is, 14 to 16% of the women who were told that Herceptin would help them had a cancer that would not respond to that drug. The laboratories produced even more false negatives: "Of those judged negative, 18% to 23% were in fact positive." An international analysis of laboratories using these tests, published online in the journal of Clinical Oncology (August 2007), indicated that false negatives were far more likely than false positives.

Various agencies in the US are working to improve accuracy. The College of American Pathologists (CAP) plans to require proficiency checks on the Her-2 test from the labs it accredits. CAP, in conjunction with the American Society of Clinical Oncology, intends to develop guidelines for the hormone-receptor test as well. The Centers for Medicare and Medicaid Services, the federal agency that regulates laboratories in the US, may update its list of laboratory tests that require outside proficiency checks to include the breast-cancer tests. Meanwhile, doctors and patients need to realize that these tests have a high rate of error. Second-opinion breast-cancer tests are often covered by major private insurers, according to The Wall Street journal.

Mathews AW. Bad cancer tests drawing scrutiny. The Wall street journal. January 4, 2008. Available at: SB11994t325367266813.html. Accessed January 1,2008.
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Title Annotation:Shorts
Author:Klotter, Jule
Publication:Townsend Letter
Geographic Code:1USA
Date:Aug 1, 2008
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