© 1999 by Oxford University Press
Journal of the National Cancer Institute, Vol. 91, No. 2, 111,
January 20, 1999
© 1999 Oxford University Press
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How Should HER2 Status Be Determined?
Testing for HER2/erbB-2 is a new and unsettled territory. In general, the two principal methods are immunohistochemistry — the use of antibodies to detect overexpression of the protein — and fluorescent in situ hybridization (FISH), which detects amplification of the gene. Each has its pros and cons, as pointed out by Debu Tripathy, M.D., University of California, San Francisco, who spoke at the San Antonio Breast Cancer Symposium last month. Immunohistochemistry is relatively inexpensive and the reagents are readily available, but there is considerable variability in results — variability among assays and, even when the same assay is used, variability in interpreting its results. Gene-based techniques, like FISH, have less variability but require specialized equipment and may be more expensive.
Studies attempting to bring some standardization to HER2 testing could involve one or more of the three HER2 tests recently approved by the Food and Drug Administration.
HercepTest: DAKO Corporation, Glostrup, Denmark, and Carpinteria, Calif. Based on immunohistochemistry, this test was developed, according to the package insert, to provide an alternative to the assay used in the clinical trials of Herceptin, the anti-HER2 breast cancer therapy recently approved by the Food and Drug Administration. When DAKO compared its antibody's results to the results of the assay used in the Herceptin clinical trial, the concordance between the two tests was 79%. It was approved by the FDA in September 1998 as an aid in the assessment of patients for whom Herceptin treatment is being considered.
INFORM HER-2/neu Test. Developed by Oncor, Inc., and recently acquired by Ventana Medical Systems, Inc., Tucson, Calif. (November 1998). A FISH assay developed to help predict breast cancer recurrence. In Oncor's clinical study, HER-2/neu was shown to have predictive power independent of the other prognostic factors evaluated (tumor size, patient age at diagnosis, tumor grade, and estrogen receptor status). Approved by the FDA in December 1997 for use as an adjunct to existing prognostic tests in patients who have had a primary, invasive, localized breast carcinoma and who are lymph node-negative.
PathVysion HER-2 DNA Probe Kit. Vysis, Inc., Downers Grove, Ill. Based on Vysis' FISH technology, this test was developed specifically for predicting a patient's response to doxorubicin, according to the company. For FDA approval, the assay was tested in patients from the Cancer and Leukemia Group B trial that evaluated three different doses of cyclophosphamide, doxorubicin, and 5-fluorouracil (see main story). Those who scored positive on the test responded better to the higher doses. Approved by the FDA in December 1998 for determining the response of patients with node-positive, stage II breast cancer to cyclophosphamide, doxorubicin, and 5-fluorouracil (CAF).
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