SPoT-Light HER2 CISH, which stands for Subtraction Probe Technology Chromogenic In Situ Hybridization, is a test used see if breast cancer cells are HER2-positive. HER2-positive cells have too many HER2 receptor proteins at the cell surface. These receptors receive signals from outside the cell telling it to grow and divide.
The SPoT-Light HER2 CISH test, which was approved by the U.S. Food and Drug Administration in 2008, looks for HER2 genes in a breast cancer tissue sample. The SPoT-Light test uses a stain that makes HER2 genes change color. After the stain is applied to the breast cancer tissue, the sample is examined with a microscope. This shows how many copies of the HER2 gene are in tumor cells. When there are extra copies of the gene, there are extra receptor proteins at the cell surface.
The SPoT-Light test can be used on fresh tissue samples or tissue samples that have been stored in wax or other chemicals, but it doesn't work on frozen tissue samples. With the SPoT-Light test, you get a score of either “HER2-positive” or “HER2-negative.”
Research has shown that some HER2 test results may be wrong. This is probably because different labs have different rules for classifying positive and negative HER2 status. Each pathologist also may use slightly different criteria to decide whether the results are positive or negative. In most cases, this happens when the test results are borderline -- meaning they aren't strongly HER2-positive or HER2-negative.
In other cases, tissue from one area of a breast cancer can test HER2-positive and tissue from a different area of the cancer can test HER2-negative.
Inaccurate HER2 test results may cause women diagnosed with breast cancer to get less than the best care possible. If all or part of a breast cancer is HER2-positive but test results classify it as HER2-negative, doctors aren't likely to recommend medicines that work against HER2-positive breast cancers -- even though the woman could potentially benefit from those medicines. If a breast cancer is HER2-negative but test results classify it as HER2-positive, doctors may recommend anti-HER2 treatments -- even though the woman is unlikely to get any benefits and is exposed to the medicines' risks.
There are three medicines that work against HER2-positive breast cancer:
- Herceptin (chemical name: trastuzumab)
- Tykerb (chemical name: lapatinib)
- Perjeta (chemical name: pertuzumab)
If your HER2 test results are HER2-negative, you may want to ask your doctor about how confident he or she is in the lab that did the HER2 testing and if another HER2 test might make sense for your unique situation.
If your HER2 test results are borderline, you might want to ask your doctor if more than one pathologist reviewed the results. If the HER2 test results weren't reviewed by more than one pathologist, you may want to ask if the results can be reviewed again.