It’s the third day of National Breast Cancer Awareness Month 2022! To recap, breast cancer isn’t a single disease. It is a collection of diseases that cause cells in the breast—specifically the cells that produce and deliver milk to nursing infants called epithelial cells—to grow uncontrollably, forming a tumor. Each breast cancer case is as unique as each person, but they can be classified based on similarities in how they look under a microscope (histology) and on the characteristics of their DNA (molecular).

Molecular breast cancer subtypes, which are crucial diagnostic tools used to determine the best and most appropriate course of treatment, include four subtypes recognized by scientists and clinicians based on their expression of hormone receptors (HR) for estrogen and progesterone (ER and PR) and their expression of the cell-surface receptor HER2: Luminal A, Luminal B, HER2-positive, and Triple Negative Breast Cancer.

Today’s post is all about the HER2-enriched (also called HER2+) subtypes, which express a cell surface protein receptor called HER2. These breast cancers have higher than normal levels of HER2 receptors, which normally tell breast cells to grow during normal development in puberty. In cancer, these receptors stay active and make breast cells grow when they shouldn’t, which is a key characteristic of breast cancer. Luminal B breast cancers have too much of the cell surface receptor HER2 in addition to having too much estrogen and progesterone receptors (ER/PR +ve), as do breast cancers that do not also express hormone receptors (HER2-enriched).

How does HER2 receptors make breast cancer cells grow? When the receptor on the surface of the cell becomes activated, it sends a signal to the cell that tells it to grow, like when your breasts are growing during puberty. Normally, after puberty, the receptor and related receptors are no longer activated and your breast cells stop growing. In breast cancer, your breast cells make too many HER2 receptors, becoming constantly activated ,making your breast cells grow abnormally, which is one hallmark of cancer. If other changes occur in your breast cells to form a cancerous growth, these HER2 receptors make the cancer cells grow uncontrollably.

HER2+ breast cancer is not as common as HR+ breast cancer, accounting for 10-20% of breast cancers. However, these breast cancers are often more aggressive and faster growing than HR+ breast cancer. They are diagnosed by a pathologist based on analysis of HER2 gene expression and HER2 proteins present in cancer cells in a biopsy and in the tumor after surgical removal. This type of breast cancer, like most breast cancers, is first treated by surgery to remove the tumor. .

Follow-up treatments include chemotherapy and HER2-targeted therapies that block the activity of HER2 on breast cancer cells, including antibody drugs that bind to HER2 receptors and cause them to be degraded by the cell as well as triggering the body’s natural immune system to attack HER2+ tumor cells. These drugs include Trastuzumab and Pertuzumab. A derivative of Trastuzumab called Ado-trastuzumab emtansine (also called T-DM1) is an antibody-drug conjugate that uses the Trastuzumab antibody to carry emtansine chemotherapy directly to breast cancer cells with high levels of HER2, targeting tumor cells and reducing damage to normal cells and tissues.

These treatments reduce the risk of the cancer from coming back, or recurring. They do come with some not-so-great side effects, which your oncologist should consider and help you with. Quality of life should always be a consideration when it comes to cancer treatment.

For more on HER2+ positive breast cancer, check out the American Cancer Association. As with other subtypes of breast cancer, early detection increases your chance of survival, so keep up with your routine mammograms and self-exams.