The U.S. Food and Drug Administration today approved a new genetic test that will help health care professionals determine if women with breast cancer are HER2-positive and, therefore, candidates for Herceptin (trastuzumab), a commonly used breast cancer treatment.

The test, called Inform Dual ISH, allows for measurement of the number of copies of the HER2 gene in tumor tissue. The HER2 gene is located on chromosome 17 in human cells. An excessive amount of the protein produced by the gene is found in some types of cancer cells, including breast cancer cells.

The Inform Dual ISH test allows lab personnel to count the number of copies of HER2 genes on chromosome 17 in a small sample of the breast tumor. The sample is stained with chemicals that cause copies of HER2 genes and chromosome 17 to change color. Copies of the HER2 gene appear black and copies of chromosome 17 appear red. These color changes can be seen under a standard microscope.

This feature allows lab personnel to see and count copies of chromosome 17 and HER2 genes on the same slide, similar to HER2 amplification measurements that have traditionally only been available using fluorescence microscopes. The Inform Dual ISH, however, allows lab staff to see the HER2 and chromosome 17 signals directly under a microscope, for longer periods of time.

The FDA based its approval of the Inform Dual ISH on a U.S. study involving tumor samples from 510 patients with breast cancer. This study showed that the test was effective in confirming that a patient’s tumor sample contained more than the normal number of copies of the HER2 gene in 96 percent of the HER2 positive tumor samples. Patients with more than the normal number of copies of the HER2 gene are considered candidates for Herceptin therapy. About 20 percent of women diagnosed with breast cancer are HER2-positive.

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