IHC (ImmunoHistoChemistry) Tests
Updated on January 2, 2024
IHC, or ImmunoHistoChemistry, is a special staining process performed on fresh or frozen breast cancer tissue removed during biopsy. IHC is used to show whether or not the cancer cells have HER2 receptors and/or hormone receptors on their surface. This information plays a critical role in treatment planning.
IHC for HER2 testing
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. With too many HER2 receptors, the cells receive too many signals telling it to grow and divide.
The IHC test gives a score of 0 to 3+ that measures the amount of HER2 receptor protein on the surface of cells in a breast cancer tissue sample. If the score is 0 to 1+, it’s called HER2 negative. If the score is 2+, it's called borderline. A score of 3+ is called HER2 positive.
We know that a large number of breast cancers considered HER2-negative have some HER2 proteins on the surface of its cells. There just aren’t enough HER2 proteins for the cancer to be considered HER2-positive. Doctors now consider these cancers HER2-low.
HER2-low breast cancer has a 1+ score on an IHC test or a 2+ score on an IHC test plus a negative FISH test.
IHC test results are most reliable for fresh or frozen tissue samples. IHC tends to be an unreliable test for tissue that's preserved in wax or other chemicals.
IHC for hormone receptor testing
Most testing labs use the IHC test to see if there are hormone receptors on breast cancer cells. If hormone receptors are present, this means that the cancer cells’ growth is fueled by the hormones estrogen and/or progesterone.
Not all labs use the same method for analyzing the results of the test, and they do not have to report the results in exactly the same way. So you may see any of the following results:
a percentage that tells you how many cells out of 100 stain positive for hormone receptors. You will see a number between 0% (none have receptors) and 100% (all have receptors)
a number between 0 and 3. “0” means that no receptors are present, “1” a small number present, “2” a medium number, and “3” a large number
an Allred score between 0 and 8. This scoring system is named for the doctor who developed it. The system looks at the percentage of cells that test positive for hormone receptors, as well as how well the receptors show up after staining (this is called “intensity”). This information is combined to give a score between 0 and 8. The higher the score, the more receptors were found and the easier they were to see in the sample.
the word “positive” or “negative”
Keep in mind that a test should be done for both estrogen receptors and progesterone receptors.
If your result is reported as just the word positive or negative, ask your doctor for a more definite percentage, rating, or other number. Different labs have different cutoff points for calling the cancer either hormone-receptor-positive or hormone-receptor-negative. For example, if less than 10% of your cells stain positive (fewer than 1 in 10), one lab might call this a negative result. Another lab might consider this positive, even though it is a low test result. Research studies have shown that any positive result, no matter how low, suggests that hormonal therapy could help treat the cancer. A score of 0 is needed to completely rule out hormonal therapy as a treatment option.
There are several types of hormonal therapy medicines.
Sometimes, a report will come back from the laboratory saying that the hormone status is unknown. This can mean one of several things:
The test was never ordered or done.
The sample of tissue that the laboratory received was too small to get reliable results.
Few estrogen and progesterone receptors were present.
If there are no hormone receptors present, or they cannot be measured or seen, the cancer is called hormone-receptor-negative.
Talk with your doctor to make sure that your test is done by a laboratory with a great deal of experience in IHC testing for hormone receptors. The more tests the lab does, the more accurate your results are likely to be. If you receive a negative test result, ask for a complete explanation as to why the cancer is considered hormone-receptor-negative. You also might ask to have the test redone.
