What is HER2+ metastatic breast cancer?
Breast cancer is a type of cancer that starts in the breast. It can start in one or both breasts, and it is the most common cancer in women in the US, excluding skin cancer. If the breast cancer is metastatic, it means it has spread to other parts of the body and is no longer only in the breast area.
HER2+ breast cancer is a subtype of breast cancer. HER2 is a protein that tells cells to grow. In HER2+ breast cancer, the cancer cells have too much HER2, which leads to cancer growth. These cancer cells grow and divide faster than healthy cells, causing tumors to form. About 15 to 20% of breast tumors have higher levels of HER2.
HER2+ breast cancer can spread to other parts of the body. This is known as HER2+ metastatic breast cancer (or HER2+ mBC). If it cannot be removed by surgery, the cancer is called “unresectable.”
6%
of women in the US have metastatic breast cancer when they are first diagnosed
What are the types of metastatic breast cancer (MBC)?
There are several types of breast cancer that can metastasize. Most breast cancers start in the ducts or lobules and are called:
- Invasive ductal carcinomas, which start in the cells lining the milk ducts and make up the majority of breast cancers
- Invasive lobular carcinomas, which start in the lobules—small, tube-like structures that contain milk glands
Testing may be done to determine breast cancer subtypes such as:
- Hormone receptor-positive or -negative—determines whether cells have proteins that are estrogen receptor (ER) or progesterone receptor (PR)
- HER2-positive—have many copies of the HER2 gene or high levels of HER2 protein, which is essential for tumor cell growth
- HER2-negative—has little to no HER2 protein
- HER2-low–low level of HER2 on the cancer cells but not enough HER2 to be considered HER2‑positive
- Triple-negative—Triple-negative breast cancer (TNBC) doesn’t have estrogen or progesterone receptors and also makes too little or none of the HER2 protein
Risk factors
Risk factors for developing breast cancer include:
Sex: women are much more likely than men to develop breast cancer
Aging
Personal and family history of breast cancer
Inherited genes that increase cancer risk
Radiation exposure
Obesity
Beginning period before age 12
Beginning menopause at an older age
Having a first child after age 30
Having never been pregnant
Receiving postmenopausal hormone therapy
Alcohol use
Please note that the risk factors listed above are not exhaustive.
HER2=Human epidermal growth factor receptor 2.
