TUESDAY, June 14 (HealthDay News) -- A new genetic test that helps determine if breast cancer patients are good candidates for treatment with the drug Herceptin was approved Tuesday by the U.S. Food and Drug Administration.

About 20 percent of breast cancers are HER2-positive, and respond well to Herceptin (trastuzumab).

The new Inform Dual ISH test reveals 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," Alberto Gutierrez, director of the Office of In Vitro Diagnostic Device Evaluation and Safety in the FDA's Center for Devices and Radiological Health, said in an agency news release.

The FDA's approval of the test was based on a U.S. study that included tumor samples from 510 breast cancer patients. The study found that the test was effective in confirming a higher than normal number of copies of the HER2 gene in 96 percent of the HER2-positive tumor samples.

The test was also effective in excluding the possibility that more than the normal number of copies of the HER2 gene were present in 92.3 percent of HER2-negative tumor samples, according to the FDA.

Dr. Stephanie Bernik, chief of surgical oncology at Lenox Hill Hospital in New York City, said the new test will help "in acquiring the data about a woman's cancer more quickly and efficiently. This will help speed the process of formulating a treatment plan during a time when a woman is searching for answers regarding her future.

"The faster a treatment plan is formulated, the easier it is for a woman to deal with her diagnosis. When faced with too many unknowns, the diagnosis of breast cancer can be overwhelming. Because this test can be performed in a standard lab, the information regarding HER2 status will be known quickly, and a woman will know if her treatment will be over within a few months, or might go on for a full year," Bernick said.

Dr. Freya Schnabel, director of Breast Surgery at NYU Langone Medical Center, said: HER2 testing is an "important part of the assessment of breast cancer tissue, because it tells us important information about the biology of the tumor and also helps identify the subset of patients who would benefit from treatment with Herceptin. At this point, testing for HER2/neu frequently involves two levels of testing and there is sometimes lack of agreement between test results, making a patient's status unclear."

The new test is made by Tucson, Ariz.-based Ventana Medical Systems.

More information

The American Cancer Society has more about breast cancer.