What is HER2+ breast cancer?
Some people with breast cancer have a gene mutation that causes their cells to make too much of the HER2 (human epidermal growth factor receptor 2) protein. At higher-than-normal levels, HER2 protein promotes the growth of abnormal cells—this causes HER2+ breast cancer. Among people with breast cancer, about 20%—or about 1 in 5—have HER2+ breast cancer.
HER2+ breast cancer is different from other types of breast cancer, because it:
- Tends to be more aggressive
- Grows quickly
- Is more likely to come back or spread, even after other treatments
Until there is a cure for breast cancer, there is still a risk of the cancer progressing.
What is metastatic breast cancer (mBC)?
Metastatic breast cancer—also called Stage IV or advanced breast cancer—is cancer that has spread beyond the breast and nearby lymph nodes to other parts of the body.
In nearly 1 in 4 people (25%) with breast cancer diagnosed at an early stage, the cancer will come back as advanced, or metastatic, breast cancer. In 6 to 10% of new breast cancer cases, the breast cancer is metastatic from the start. This is called de novo metastatic breast cancer.
A person's experience with metastatic breast cancer will depend on how many metastases develop and where they are in the body. Treatment can control metastatic breast cancer for some time, but often the cancer continues to grow or spread.