Breast cancer cells may have receptors (proteins) that hormones or a protein called HER2 can attach to and encourage the cells to grow. A pathologist tests the cancer cells that were taken during the biopsy or surgery for these receptors.
The results help you and your doctor decide on the most effective treatment for you.
Hormones help control how cells grow and what they do in the body. Hormones, particularly oestrogen, can encourage breast cancer cells to grow.
Breast cancer that has receptors for the hormone oestrogen is called oestrogen receptor-positive (ER-positive) breast cancer. The term ER is used because the American spelling of oestrogen is estrogen. About 70% of breast cancers are ER-positive. Hormonal therapies work well for ER-positive breast cancer.
Breast cancer that does not have hormone receptors is called oestrogen receptor-negative (ER-negative) breast cancer.
Breast cancer cells may also have receptors for the hormone progesterone (PR-positive).
Some breast cancers have too much of a protein (receptor) called HER2 (human epidermal growth factor receptor 2) on the surface of their cells. This is called HER2-positive breast cancer. The extra HER2 protein encourages the cancer cells to divide and grow.
Between 15 and 20 out of every 100 women with breast cancer (15 to 20%) have HER2-positive cancers.
Specific targeted therapy drugs are used to treat HER2-positive breast cancer. They lock on to the HER2 protein and stop the cells dividing and growing.