Tykerb can work in people with advanced-stage HER2-positive breast cancers that have stopped responding to anthracyclines, taxanes, and Herceptin. Tykerb also is used to treat postmenopausal women diagnosed with hormone-receptor-positive, HER2-positive metastatic breast cancer.
Four different tests can be used to figure out if the cancer is HER2-positive and if it will likely respond to Tykerb:
IHC is the most commonly used test to see if a tumor has too much of the HER2 receptor protein on the surface of the cancer cells.
The IHC test gives a score of 0 to 3+ that indicates the amount of HER2 receptor protein in tumors. If the tumor scores 0 to 1+, it's called "HER2 negative." If it scores 2+ or 3+, it's called "HER2 positive."
Women with IHC positive scores tend to respond favorably to Tykerb. The drug is not considered effective for tumors with IHC scores of 0 or 1+.
It's important to note that results on the IHC test may vary from lab to lab, and that some labs are more proficient at HER2 testing than others. Discuss with your doctor whether you might want to get a FISH test, especially if you have a 1+ or 2+ result from IHC. That way you can get another measure of whether the tumor might respond well to Tykerb.
The IHC test results are most reliable for fresh or frozen tissue samples. IHC tends to be an unreliable way to test tissue that's preserved in wax or other chemicals. FISH testing is the preferred way to assess preserved tissue samples.
FISH (Fluorescence In Situ Hybridization)
The FISH test looks for the HER2 gene abnormality. This test is the most accurate, but less available, way to find out if a breast tumor is likely to respond to Tykerb. The FISH test shows how many copies of the HER2 gene are in tumor cells. The more copies of the gene, the more HER2 receptors the cells have.
With the FISH test, you get a score of either "positive" or "negative" (some hospitals call a negative test "zero"). If the cancer is FISH positive, it will probably respond well to Tykerb.
SPoT-Light HER2 CISH (Subtraction Probe Technology Chromogenic In Situ Hybridization)
The SpoT-Light HER2 CISH test looks for HER2 genes in a breast cancer tissue sample. It was approved by the U.S. Food and Drug Administration in 2008. The SpoT-Light test uses a stain that makes HER2/neu genes change color. The stain is applied to the breast cancer tissue sample and looked at with a microscope. This shows how many copies of the HER2 gene are in tumor cells. The SPoT-Light test is less complicated than the FISH or IHC tests. 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 "positive" or "negative." If the cancer is SPoT-Light positive, it will probably respond well to Tykerb.
Inform HER2 Dual ISH (In Situ Hybridization)
The Inform HER2 Dual ISH test uses a special stain that makes HER2 proteins change color. The stain is applied to the breast cancer tissue sample and viewed under a microscope. The Inform HER2 Dual ISH test can be used on tissue samples that have been stored in wax or other chemicals. This test offers more precise results than the IHC HER test. It is also less expensive and doesn’t need the special microscope of the FISH HER2 test.
With the Inform HER2 Dual ISH test, you get a score of either “HER2 positive” or “HER2 negative.”