Have you been told you have HER2 positive breast cancer? Most breast cancer patients know three things about their cancer: stage, ER/PR status, and HER2 status. You know these things because they are the factors that determine what treatment you get. The stage tells us how aggressive to be with treatment. The hormone receptor status (ER/PR) tells us whether or not you need hormone blockers. The HER2 status tells us whether or not you need a therapy that is targeted at the HER2 receptor which is usually Herceptin®, also known as trastuzumab. About 15% to 20% of all invasive breast cancers are HER2 positive.
What is HER2?
Just what is HER2? HER2 is an oncogene, and oncogenes often make proteins that promote the development of cancer or make cancers more aggressive. The HER2 oncogene makes the HER2 protein. This protein is a receptor that sits on the surface of normal breast cells. Signals that are sent through this receptor are important for normal cell growth and development. The trouble comes when you have too many of these receptors (usually as a result of too many copies of the HER2 gene). When you have too many HER2 receptors on a breast cancer cell, it makes the cancer more aggressive. It is more likely to grow faster and spread.
That’s the bad news. The good news is that we have very specific targeted therapies for HER2 positive breast cancer. These therapies block the HER2 receptor so that the signals that make the cancer more aggressive are blocked. In addition, anti-HER2 therapy may make it easier for your immune system to identify and kill the cancer cell. If you receive anti-HER2 therapy, your prognosis is probably just as good as someone with HER2 negative breast cancer.
All breast cancers should be tested for HER2. There are two common ways that these tests are done. The initial test is usually done by identifying HER2 receptors on the surface of breast cancer cells with a special stain. This is called immunohistochemical staining or IHC. The pathologist then looks at the cancer cells and determines whether the amount of staining is 0 to 1+, 2+, or 3+. A score of 0 to 1+ is negative and a score of 3+ is positive. If the score is 2+, then another test is usually needed to determine if there are too many copies of the HER2 gene. This test is called FISH or fluorescence in situ hybridization. Here the pathologist can actually look at the number of copies of the HER2 gene and tell if there are too many.
HER2 Positive Treatment
If you have HER2 positive breast cancer, you will most likely receive a year of Herceptin®. Some patients with larger tumors or with involved lymph nodes may get an additional anti-HER2 therapy called Perjeta® (or pertuzumab). Other anti-HER2 therapies that you may hear about are neratinib, lapatinib, and Kadcycla®. Kadcycla® is an interesting therapy because it is actually a combination of a drug and a monoclonal antibody. The antibody finds the HER2 receptor, attaches to it, and releases the chemotherapy drug into the cell. These therapies may be used with more aggressive breast cancers, cancers that have recurred, or cancers that have spread beyond the breast (metastatic). Some of these therapies are used to treat cancers other than breast cancer that also overexpress HER2.
What is HER2 positive breast cancer? It is a breast cancer that has an overexpression of the HER2 oncogene. Because of this overexpression, the cancer makes too much HER2 receptor protein which makes the cancer more aggressive. With targeted anti-HER2 therapy like Herceptin®, the prognosis is similar to HER2 negative breast cancer. Every invasive breast cancer should be tested for HER2 overexpression to determine whether or not anti-HER2 therapy is needed.