This test looks for several types of receptors on cells in a sample of breast cancer tissue.
Fifty percent to 70% of breast cancers depend on the hormone estrogen to grow. A few breast cancers can grow without estrogen. The cancer cells that depend on estrogen make many estrogen receptors (ER), progesterone receptors (PR), or both. These receptors grab onto the hormones that float freely in your blood and use them as fuel to help the cancer grow.
Cancers that contain ERs are called ER-positive (ER+). Cancers that contain PRs are called PR-positive (PR+). Cancers with these types of receptors are called "hormone responsive" cancers.
The immunohistochemical (IHC) test also looks for cell receptors that hold onto HER2, or human epidermal growth factor type 2. HER2 is a protein that is found in excessive amounts in about 20 percent of breast cancers. HER2-positive cancers have many receptors that hold HER2 and are more aggressive than cancers that don't have a lot of HER2.
Before your healthcare provider can figure out what type of cancer treatment is best for you, he or she must look at the ERs and PRs and know your HER2 status.
To do this, your provider sends the tissue sample to a lab. There, a pathologist runs tests on the tissue sample and looks at the cells under a microscope.
You might have this test if you have breast cancer and your healthcare provider needs more information about the type of breast cancer you have.
If you have a hormone responsive cancer, you will most likely be helped by treatments that will block estrogen from attaching to the receptors or that will lower total estrogens in your system. If you are HER2-positive, you will be offered treatment with trastuzumab, pertuzumab, or lapatinib.
Your healthcare provider may also order other tests to help diagnose and treat your breast cancer. These tests include:
Blood tests. A complete blood count, or CBC, will check to see whether your blood counts are normal. Chemical and enzyme tests will check to see whether your organs are working the way they should.
21-gene. This test, also called Oncotype DX, will help your healthcare provider decide whether you need chemotherapy.
Lymph node needle biopsy. It's common for breast cancer to spread to nearby lymph nodes. If your healthcare provider feels that your lymph nodes are enlarged or different in any way, he or she will do a needle biopsy. Whether the nodes are positive for cancer will help your provider figure out or refine your treatment plan.
Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your healthcare provider.
If your results are positive for estrogen receptors, it means you are ER+. If your results are positive for progesterone receptors, it means you are PR+. In either case, hormone, or endocrine, therapy will likely decrease the chance that your cancer will grow or return. If your tumor, or tissue sample, does not show hormone receptors, you are ER-negative, PR-negative, or negative for both. In that case, hormone therapy will most likely not be helpful to you.
IHC results for HER2 are reported as 0, 1+, 2+, or 3+. A result of 0, 1+, or 2+ is considered HER2-negative (HER2-). A result of 3+ is considered HER2-positive (HER2+).
Your healthcare provider will review your results together to figure out the best therapy for you. It could be hormone therapy, chemotherapy, or other medicines that target HER2.
This test requires a sample of tissue. Most often the tissue is taken from the suspicious area of your breast during a biopsy procedure. A biopsy can be done in several ways:
Fine needle aspiration, or FNA. Your doctor will use a needle thinner than those used for blood tests. He or she will guide the needle to the area and remove a small amount of the tissue or liquid. Because the needle is so fine, you won't need any local anesthetic.
Core needle biopsy. Your doctor will use a larger needle to remove a cylinder shape of tissue from the area. Usually several samples will be removed. You will likely have a local anesthetic to ease any discomfort.
Vacuum-assisted biopsy. Your doctor will first numb the skin. He or she will then make a quarter-inch cut and insert a hollow probe. He or she will vacuum up a cylinder of tissue through a hole in the side of the probe while a rotating knife cuts the tissue. Several samples may be taken from the same cut. You won't need stitches.
Surgical open biopsy. Under certain circumstances, your doctor may use surgery to remove all or part of an abnormal area. This procedure is usually done under light sedation and with local anesthesia. But it can also be done under general anesthesia so you will sleep through the procedure.
A biopsy carries a slight chance of infection afterward. Ask your healthcare provider about warning signs to look for, such as fever, pain, or swelling.
Hormone therapy for birth control or as hormone replacement may affect your results.
You may need to temporarily stop taking hormone medicine. Also be sure your healthcare provider knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illicit drugs you may use.