When diagnosed with secondary breast cancer, all of the medical terminologies can be very overwhelming. This three part series of posts will tell you a little bit more about the main classifications of secondary breast cancer that are used to direct medical treatments. This post focuses on HER2 status.
HER2 stands for Human epidermal growth factor receptor-2. HER2 is a receptor that sits at the surface of cells and is involved in the transmission of signals that control normal cell growth. Non-cancerous cells have low levels of HER2 at the cell surface. Additionally, in general, non-cancerous cells would only have two copies of the HER2 gene that codes for the HER2 receptor. However, in approximately 15–30% of breast cancers the HER2 gene can be amplified in number (sometimes 25–50 copies of the HER2 gene could be present), and the HER2 receptor can subsequently be overexpressed resulting in 40–100 times more HER2 receptors at the breast cancer cell surface [1]. Having abnormally high levels of HER2 receptors is associated with the higher levels of cell growth that occurs in cancers.
Breast cancer cells that contain these amplified levels of HER2 are known as HER2 positive or HER2+. Conversely, if HER2 is not amplified the breast cancer would be classified as HER2 negative or HER2-.
Tissue samples from a biopsy are tested in a laboratory to determine HER2 status. A technique known as Immunohistochemistry (IHC) is used to measure the HER2 levels in the biopsy sample. A score of 0 or 1+ is considered HER2 negative, a score of 3+ is regarded as HER2 positive and a score of 2+ is regarded as equivocal [1]. Your oncologist will be able to inform you of your score and explain what these results mean to you.
Knowing HER2 status is important because numerous breast cancer treatments target the HER2 receptor with the aim of blocking these growth signals and/or targeting chemotherapy to the breast cancer cells. If you are HER2 negative these treatments will not work for you and your oncologist will suggest alternative treatments.
Examples of HER2 targeted breast cancer treatments include Trastuzumab (which is also known as Herceptin®) and Trastuzumab emtansine (which is also known as Kadcyla® and TDM1). Trastuzumab will bind to HER2 and block the HER2 receptor and subsequently reduce the signals for cancer cell growth. Trastuzumab emtansine will bind to HER2 and deliver emtansine (a type of chemotherapy) to the cancer cells in a more targeted manner.
Some HER2+ positive tumours can lose HER2 overexpression after treatment with Trastuzumab. Conversely, some initially HER2 negative tumors can become HER2+ over time. Additionally, in the case of secondary breast cancer the HER2 status of the initial breast biopsy can be different to the site the breast cancer spreads too. A biopsy of the site the breast cancer has spread to will help determine the HER2 receptor status of the secondary breast cancer and subsequent treatment options.
It's ok to feel confused when presented with your breast cancer classification and please do not be afraid to ask your oncologist or secondary breast cancer nurse to explain your pathology results to you.
Remember when it comes to your diagnosis - knowledge is power!
References:
[1] Gutierrez & Schiff 2011. HER 2: Biology, Detection, and Clinical Implications. Arch Pathol Lab Med. 2011 Jan; 135(1): 55–62.
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