HER2/neu status

HER2/neu status
About 1 of 5 breast cancers have too much of a growth-promoting protein called
HER2/neu (often just shortened to HER2). The HER2/neu gene instructs the cells to
make this protein. Tumors with increased levels of HER2/neu are referred to as HER2-
positive.
Women with HER2-positive breast cancers have too many copies of the HER2/neu gene,
resulting in greater than normal amounts of the HER2/neu protein. These cancers tend to
grow and spread more aggressively than other breast cancers.
All newly diagnosed breast cancers should be tested for HER2/neu because HER2-
positive cancers are much more likely to benefit from treatment with drugs that target the
HER2/neu protein, such as trastuzumab (Herceptin®) and lapatinib (Tykerb®). See the
section, "How is breast cancer treated?" for more information on these drugs.
Testing of the biopsy or surgery sample is usually done in 1 of 2 ways:
· Immunohistochemistry (IHC): In this test, special antibodies that identify the
HER2/neu protein are applied to the sample, which cause cells to change color if
many copies are present. This color change can be seen under a microscope. The test
results are reported as 0, 1+, 2+, or 3+.
· Fluorescent in situ hybridization (FISH): This test uses fluorescent pieces of DNA
that specifically stick to copies of the HER2/neu gene in cells, which can then be
counted under a special microscope.
Many breast cancer specialists feel the FISH test is more accurate than IHC. However, it
is more expensive and takes longer to get the results. Often the IHC test is used first. If
the results are 1+ (or 0), the cancer is considered HER2-negative. People with HER2-
negative tumors are not treated with drugs (like trastuzumab) that target HER2. If the test
comes back 3+, the cancer is HER2-positive. Patients with HER2-positive tumors may be
treated with drugs like trastuzumab. When the result is 2+, the HER2 status of the tumor
is not clear. This usually leads to testing the tumor with FISH. Some institutions also use
FISH to confirm HER2 status that is 3+ by IHC and some perform only FISH.
A newer type of test, known as chromogenic in situ hybridization (CISH), works
similarly to FISH, by using small DNA probes to count the number of HER2 genes in
breast cancer cells. But this test looks for color changes (not fluorescence) and doesn't
require a special microscope, which could make it less expensive. Right now, it is not
being used as much as IHC or FISH.