What tests can detect HER2-positive breast cancer?

For women with breast cancer, there are two tests for human epidermal growth factor receptor 2 (HER-2) -- a gene that helps control how cells grow, divide and repair, themselves:
  • IHC Test (immunohistochemistry): The IHC test uses antibodies to identify HER-2. The tumor can be scored as (negative), 1+ (negative), 2+ (borderline), or 3+ (positive) on the IHC test.
  • FISH Test (fluorescence in situ hybridization): The FISH test is good for all kinds of tissue: fresh, frozen and those kept in wax. The results are (negative) or positive on the FISH test.
Only tumors that test IHC "3+" or FISH "positive" respond well to antibody therapy.
Testing for HER2-positive breast cancer begins with testing for breast cancer in general. If you have a suspicious lump, mass or other lesion in your breast your doctor will take a sample of the tissue by doing a fine needle aspiration, a needle biopsy or surgical biopsy.

If the initial biopsy shows that the tissue is cancerous, the sample should be tested further for HER2 -- a protein, produced by HER2 genes, that is present in high amounts in people who have HER2-positive breast cancer. HER2 protein causes cancer cells to grow and spread more quickly, which makes HER2-positive breast cancer an aggressive form of breast cancer.

Tests that are used for examining breast tissue for HER2 include:
  • IHC (Immunohistochemistry) measures the amount of HER2 protein in a tissue sample. IHC is the most commonly used initial test for HER2 in breast cancer samples. However, it sometimes doesn't give a definite answer.
  • FISH (Fluorescent in situ hybridization) is a test that flags HER2 genes with fluorescent pieces of DNA so that the genes can easily be counted under a special microscope. FISH is often done as a follow-up after an IHC test.
  • CISH (chromogenic in situ hybridization) works similarly to FISH to count the HER2 genes, but looks at color changes in the cells rather than fluorescence and doesn't require a special microscope. 
  • Dual ISH (in situ hybridization) uses a special stain to cause a color change in HER2 proteins in a tissue sample. The sample can then be examined under a regular microscope. Research shows it can be more precise than the IHC test and less costly and simpler to use than the FISH test.
If one of these tests determines that you have HER2-positive breast cancer, your doctor can prescribe medication that treats this kind of breast cancer more specifically and more successfully than drugs used for other types of breast cancer.

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