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The U.S. Food and Drug Administration recently approved a new genetic test for determining whether patients with breast
cancer are good candidates for treatment with the drug Herceptin
(generic name, trastuzumab). Herceptin has been shown to be effective in helping treat breast cancer but it only
works in patients with certain types of breast cancers-called HER2/neu positive breast cancer. The new test,
called the SPOT-Light HER2 CISH kit, may be more convenient than the two other FDA-approved tests, the
fluorescent in situ hybridization (FISH) and immunohistochemistry (IHC), because it can be performed
with a standard microscope, which allows more medical facilities to perform the test. The new
test can also allow laboratories to store a patient's tissue for future reference.
HER2 (human epidermal growth factor receptor 2) is a protein found on the surface of cells that, when
functioning normally, has been found to be a key component in regulating cell growth. However, when
the HER2 protein is altered, extra HER2 protein receptors may be produced. This over-expression of
HER2 causes increased cell growth and reproduction, often resulting in more aggressive breast
cancer cells. Women with HER2 over-expression may not be as responsive to standard breast cancer
treatments, including certain regimens of chemotherapy.
Herceptin works by targeting breast cancer cells that have too many copies of the HER2 protein. After
it has identified which cells over-express the HER2 protein, Herceptin attaches itself to the
HER2 protein receptors on the surface of these cells. By binding to the cells, Herceptin
slows the growth and spread of tumors that have an overabundance of HER2. Many experts
believe that Herceptin represents the future direction of breast cancer drugs in that
it targets a particular protein of the cancer cell and prevents it from carrying out
its action. The drug, Tykerb, is
newly approved by FDA and is typically used in patients who have already been treated with Herceptin.
The SPOT-Light HER2 CISH kit is a test that measures the number of copies of the HER2 gene in
tumor tissue. "When used with other clinical information and laboratory tests, this test can
provide health care professionals with additional insight on treatment decisions for patients with
breast cancer," said Daniel Schultz, M.D., director of the FDA's Center for Devices and
Radiological Health," in an FDA news release.
According to the FDA, the SPOT-Light test counts the number of HER2 genes in a small sample of
removed tumor. The removed piece is stained with a chemical that causes any HER2 genes in the
sample to change color. This color change can be visualized under a standard microscope, eliminating
the need for the more expensive and complex fluorescent microscopes required to read assays
already on the market. Unlike existing tests, the SPOT-Light allows labs to store the tissue for future reference.
The FDA's approval of the SPOT-Light test came after reviewing the results of a study using tumor
samples from patients with breast cancer in the United States and Finland. According to the FDA, these
studies confirmed that the test was effective in determining how many HER2 genes were in these patients.
The SPOT-Light test should be available in mid-August. Patients eligible for HER2 testing should talk
to their physicians about whether this test is an option for them.
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