IHC Tests (ImmunoHistoChemistry)

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 receptors, the cells receive too many growth signals. The medication Herceptin (chemical name: trastuzumab) works by blocking these receptors and preventing the growth signals from getting through to the cancer cell.

The IHC test gives a score of 0 to 3+ that indicates the amount of HER2 receptor protein on the cells in a sample of breast cancer tissue. If the tissue scores 0 to 1+, it’s called “HER2 negative.” If it scores 2+ or 3+, it’s called “HER2 positive.”

People with HER2-positive scores tend to respond favorably to Herceptin. The medication 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 experienced with testing for HER2 than others. Talk to your doctor about the possibility of also getting a FISH test, which uses another technology for measuring HER2 — 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 Herceptin.

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.

IHC for hormone receptor testing

Most testing labs use the IHC staining process to make any hormone receptors show up on the cells in sample of breast cancer tissue. If hormone receptors are present, this means that the cancer cells’ growth is fueled by the female hormones estrogen and/or progesterone. The cancer is likely to respond to hormone therapies such as tamoxifen and aromatase inhibitors, which block the action of estrogen or lower estrogen levels in the body.

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 when you get your results back:

• 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 what percentage of cells test positive for hormone receptors, along with how well the receptors show up after staining (this is called “intensity”). This information is then combined to score the sample on a scale from 0 to 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 hormone therapy could be of benefit. A score of “0” is needed to completely rule out hormone therapy as an option.

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 a sample of the tumor tested again.