© 2000 by Oxford University Press
Journal of the National Cancer Institute, Vol. 92, No. 4, 293,
February 16, 2000
© 2000 Oxford University Press
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Common Techniques Used to Detect HER2
HER2, human epidermal growth factor receptor-2, is a transmembrane glycoprotein found in normal cells. Binding of a growth factor to HER2 activates the receptor, which transmits growth signals from the outside of the cell to the nucleus and stimulates the expression of certain genes that control aspects of normal cell division.Overexpression of HER2 occurs in 25% to 30% of breast cancers as well as in ovarian, endometrial, gastric, lung and salivary gland tumors to varying degrees. The HER2 gene is amplified in about 90% of breast tumors that overexpress the protein. Overexpressing cells with an altered gene contain anywhere from 10 to 100 times the number of receptors than normal cells.
The most widely used technique to measure HER2 protein is IHC. An antibody is used to probe for HER2 in tumor cells and is visualized by attaching a color-emitting substance. The advantage of IHC is that it can be easily carried out on formalin-fixed, paraffin-embedded tissue, (the form in which tissue from clinical trials is commonly preserved) as well as frozen samples, and the technique is more familiar, less expensive, and simpler compared with FISH. In addition, the equipment required for IHC is commonly found in hospitals and clinical laboratories. Several antibodies are available, including mouse monoclonal as well as goat and rabbit polyclonal sera.
FISH, the second most common technique, measures HER2 gene amplification. A DNA probe complementary to a small portion of the HER2 gene is used to search the tumor cell DNA. A fluorescent signal attached to the probe, enables detection of the HER2 sequence with a fluorescence microscope. The tumor cells are scored by counting the percentage of tumor cells with HER2 gene amplification. The scoring of FISH signals requires careful counting of the number of fluorescent loci in 40 to 100 cells, a relatively time-consuming process, and is done with a fluorescence microscope not commonly found in many pathology laboratories.
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