A test that measures the number of copies of the HER2 gene in breast tumor tissue has been approved by the Food and Drug Administration, the agency announced on June 14.

If the Inform Dual ISH test is positive, then the patient is a candidate for treatment with trastuzumab, the recombinant monoclonal antibody directed against HER2 that is marketed as Herceptin by Genentech for the treatment of HER-2 overexpressing breast cancer.

The test is manufactured by Tucson, Ariz.–based Ventana Medical Systems, a member of the Roche group, as is Genentech.

"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, Ph.D., director of the Office of In Vitro Diagnostic Device Evaluation and Safety in the FDA’s Center for Devices and Radiological Health, said in the statement announcing the approval.

The test makes it possible "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 statement said. But the new test, "allows lab staff to see the HER2 and chromosome 17 signals directly under a microscope, for longer periods of time."

Approval is based on a study conducted in the United States that evaluated the test in 510 women with breast cancer. The test confirmed that the tumor sample contained more than the normal number of copies of the HER-2 gene, located on chromosome 17, in 96% of the HER-2 positive samples, according to the statement.

The test also excluded the possibility that an excessive number of HER2 genes was present in 92.3% of the HER2-negative samples.

About 20% of women diagnosed with breast cancer are HER2-positive, according to the FDA.