In June 2011, the U.S. Food and Drug Administration (FDA) approved a new test called Inform Dual ISH to determine the HER2 status of breast cancer cells. ISH stands for "in situ hybridization."
HER2-positive breast cancers make too much of the HER2 protein, which receives signals telling the breast cancer to grow. About one out of every four breast cancers is HER2-positive.
HER2-positive breast cancers tend to be more aggressive than HER2-negative breast cancers. Herceptin (chemical name: trastuzumab) and Tykerb (chemical name: lapatinib) are targeted therapy medicines used to treat HER2-positive breast cancers. Figuring out the HER2 status of a breast cancer is an important first step in deciding on a treatment plan. Still, research has shown that HER2 testing, as well as the way the test results are recorded in medical and insurance records, is often inconsistent and sometimes inadequate.
Before FDA approval of the new Inform Dual ISH test, there were three main tests to determine a breast cancer's HER2 status: IHC, FISH, and SPoT-Light CISH.
- IHC (immunohistochemistry) uses a tissue stain and a microscope to detect excess HER2 protein on the cells of a breast cancer. IHC is the most common HER2 status test, but it's not completely reliable. Experts recommend that an HER2 FISH test be done if an IHC test result is "borderline."
- FISH (fluorescence in situ hybridization) uses a fluorescence marker to detect high levels of the HER2/neu gene in breast cancer cells. FISH is a more precise -- and more expensive -- HER2 test that requires a special fluorescence microscope to measure numbers of HER2/neu genes. FISH testing is not as widely available as IHC testing, but is much more reliable than IHC. FISH is the preferred HER2 test.
- SPoT-Light CISH (subtraction probe technology chromogenic in situ hybridization) uses a special tissue stain to mark the HER2/neu genes in a way that can be seen under a standard microscope. SPoT-Light CISH was approved by the FDA in 2008 and also isn't as widely available as IHC testing. Still, like FISH, SPoT-Light CISH is a more reliable HER2 test than IHC.
The new Inform Dual ISH test offers the precision of the FISH test, but like SPoT-Light CISH doesn't need fluorescence marking or a fluorescence microscope to measure numbers of HER2/neu genes. Instead the test uses a special tissue stain to mark the HER2/neu genes in a way that can be seen under a regular microscope.
Doctors hope the Inform Dual ISH test will be a good HER2 testing option for labs, offering greater precision than IHC without the added cost and special equipment required by FISH. Still, it will likely be some time until many labs adopt the Inform Dual ISH technique for HER2 testing.
If you've been diagnosed with breast cancer, the information in your pathology report -- including HER2 status -- gives your doctor important details about the "personality" of the cancer. Knowing all the cancer's details is necessary to develop a treatment plan that makes the most sense for your specific situation.
Take the time to ask your doctor about ALL the information in your pathology report. Ask your doctor about any missing or incomplete information and any assumptions that are being made that could influence treatment decisions. Make sure HER2 testing was done and ask which type of test was performed. If only an IHC test was done, a reading of 0 or 1+ is considered negative. A 3+ reading is considered positive. If your IHC result is 2+ (which is considered borderline), ask about having a FISH test, SPoT-Light CISH test, or the new Inform Dual ISH test done to more precisely determine the cancer's HER2 status.
The Breastcancer.org Your Diagnosis pages have more details about the information that should be in your report, as well as more on HER2 status and testing.