A new genetic test that will help health care providers determine whether women with breast cancer are eligible for treatment with trastuzumab (Herceptin) has been approved by the FDA (www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/ucm259055.htm).

Inform Dual ISH (Ventana Medical Systems, Tucson, Arizona) allows for measurement of the number of copies of the HER2 gene in tumor tissue. Women with HER2-positive breast cancer can benefit from Herceptin. Approximately 20% of women diagnosed with breast cancer are HER2-positive.

Using the new test, lab personnel can count copies of the HER2 gene on chromosome 17 in a small sample of the breast tumor. A chemical stain causes copies of the HER2 gene to appear black and copies of chromosome 17 to appear red. These color changes can be seen under a standard microscope on the same slide, similar to HER2 amplification measurements that have traditionally only been available using fluorescence microscopes.

In a study of 510 women with breast cancer, the Inform Dual ISH test effectively confirmed abnormally high numbers of copies of the HER2 gene in 96% of the HER2-positive tumor samples. The test also was able to exclude the possibility of the presence of more than the normal number of copies of HER2 in 92.3% of the HER2-negative tumor samples.