What is HER2-Low 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 is a protein that tells cells to grow. When cells produce too much HER2, they can become cancerous.
Previously, doctors diagnosed breast cancer as either HER2-positive or HER2-negative. Now, they can diagnose another status: HER2-low. Having HER2-low means that there is a low level of HER2 on the cancer cells but not enough HER2 to be considered HER2-positive. Doctors have discovered that HER2-low breast cancer is common.
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). People with low levels of HER2 can be either HR+ (hormone receptor-positive) or HR- (hormone receptor-negative)
- 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.
