Some breast cancer cells have receptors, which allow particular hormones or a protein called HER2 to attach to the cells and encourage them to grow. Your doctors need to know if the cancer cells have high levels of these receptors to help them plan the most effective treatment for you.
If you have already had treatment for breast cancer a sample of breast cancer cells (from a biopsy or surgery) will usually have been tested for these receptors. But you may also have a biopsy taken from the secondary cancer because the hormone or HER2 receptors may be different from the primary cancer. Your cancer specialist will advise you if this is appropriate in your situation.
If you haven’t been treated for breast cancer before, your doctor will, if possible, take a biopsy of the secondary cancer. The cancer cells are tested to find out which receptors are present.
Some cancers have receptors for the hormones oestrogen and progesterone. Hormones act as chemical messengers and influence how cells grow and what they do.
Breast cancer that has oestrogen receptors is known as oestrogen-receptor positive or ER positive. Breast cancer that doesn’t have oestrogen receptors is known as ER negative. (ER is used because of the American spelling of oestrogen as estrogen.)
If the cancer is ER positive it usually responds well to treatment with hormonal therapies.
Some cancers have receptors for a protein known as HER2 (human epidermal growth factor 2). Cancers with high levels of HER2 receptors are called HER2 positive. Treatments known as targeted therapies such as trastuzumab (Herceptin®) are used to treat women with HER2 positive breast cancer.
Nowadays all women diagnosed with breast cancer have the cancer cells tested for HER2 receptors. If this didn’t happen when you were first diagnosed with breast cancer you will now have it done. If possible, a biopsy will be taken from the secondary cancer but cells from previous biopsies, or surgery can also be used for testing.