Last Updated: 2001-05-11 18:00:25 EDT (Reuters Health) - In the selection of breast cancer patients for trastuzumab therapy, fluorescence in situ hybridization (FISH) may be more accurate and reliable than the HercepTest, according to a study reported in the May 15th issue of the Journal of Clinical Oncology.
Dr. Raymond R. Tubbs of the Cleveland Clinic Foundation and colleagues assessed 400 infiltrating ductal carcinomas for overexpression of Her-2/neu using the HercepTest and monoclonal CB11 immunohistochemistry. Of the 400 samples, 145 were also evaluated with direct- and digoxigenin-labeled FISH, and 144 by autoradiographic RNA:RNA in situ hybridization.
The results of CB11 and the HercepTest were discordant in 47 cases (12%). Compared with direct-label FISH, CB11 results were false-positive in 16 cases and HercepTest results were false-positive in 28 cases.
"Among immunohistochemistry false-positive cases, 26 of 28 HercepTest and 14 of 16 CB11 false-positive cases did not overexpress Her-2/neu mRNA as measured by in situ hybridization," the researchers report. "Most CB11 and HercepTest false-positive cases were scored 2+ rather than 3+, and all 2+ false-positive cases were mRNA-negative."
In contrast to immunohistochemistry, the results of direct- and digoxigenin-labeled FISH "were highly concordant," with only one discrepancy between the tests remaining unexplained.
Dr. Tubbs and his associates note that, according to year 2000 American Cancer Society statistics, a 12% false-positive rate on the HercepTest would cause more than 20,000 cases in the US to be misclassified. "We advocate a voluntary or US Food and Drug Administration-mandated withdrawal of the 2+ HercepTest score as a criterion for Herceptin therapy and recommend a diagnostic algorithm whereby all immunohistochemistry-positive cases are confirmed by FISH."
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