The US Food and Drug Administration (FDA) 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 tumour 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 tumour. The sample is stained with chemicals that cause copies of HER2 genes and chromosome 17 to change colour. Copies of the HER2 gene appear black and copies of chromosome 17 appear red. These colour 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.

“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 Alberto Gutierrez, Ph.D., director of the Office of In Vitro Diagnostic Device Evaluation and Safety in the FDA’s Centre for Devices and Radiological Health.

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

The study also showed that the test was effective at excluding the possibility that more than the normal number of copies of the HER2 gene were present in 92.3 percent of the HER2 negative tumour samples. Patients who do not have more than the normal number of copies of the HER2 gene are typically not candidates for Herceptin therapy. The ability to identify patients who are HER2-positive is a useful tool for physicians who may be considering treatment with Herceptin for their breast cancer patients.

Breast cancer is the second leading cause of cancer-related death among women. An estimated 207,090 new cases of breast cancer were diagnosed in the United States during 2010 and about 39,840 women died from the disease, according to the National Cancer Institute. About 20 per cent of women diagnosed with breast cancer are HER2-positive.

Tuscon, Arizona-based Ventana Medical Systems manufactures the Inform Dual ISH test. Herceptin is marketed by South San Francisco based-Genentech, a member of the Roche Group.