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Breast cancer cells sometimes have what are called receptors, which are tiny molecules of protein. Hormones may attach to specific receptors and trigger actions within the cell. Some types of cancerous, or malignant, breast tumors have cell receptors to which the hormone estrogen attaches, stimulating the cells to grow. In the case of estrogen receptor-negative breast cancer, or ER-negative breast cancer, the cells do not have hormone receptors for estrogen. The presence or absence of estrogen receptors makes a difference to breast cancer treatment, because, with estrogen receptor-positive tumors, hormone therapies can be used which block the receptors, slowing breast cell growth.
A number of different hormone receptors may be found on breast cancer cells. As well as receptors specific to estrogen, other receptors may be present for the hormone progesterone or for a protein known as HER2. When receptors are found, treatments may be given using drugs which target those receptors and act against cancer growth. Some tumors will not show any of the receptors, in which case they are described as triple negative. As estrogen receptor-negative breast cancer does not respond to the body's progesterone or estrogen levels, it is not usually possible to treat it using hormone therapies.
In order to find out whether a breast tumor contains cells with receptors, a small sample of tissue, known as a biopsy, is normally taken and studied under a microscope. Different methods may be used to take a biopsy but most commonly, after numbing the area, a needle is used to cut out a core of tissue. In cases where the tumor is too small to feel, imaging techniques such as ultrasound scanning may be used to guide the needle into place. If a tumor is found to consist of estrogen receptor-negative breast cancer cells, the treatment plan will also depend on the size of tumor, how aggressive it is and whether it has spread.
When an estrogen receptor-negative breast cancer has not yet spread throughout the body, it is normally treated using surgery. This could involve removing all of the breast or just the area containing the tumor. Radiotherapy may be used after the surgery to kill off any remaining tumor cells, and chemotherapy could also be given to prevent the cancer from recurring.
Sometimes, chemotherapy, which uses drugs to destroy cancer cells, is given before surgery so that the tumor reduces in size. Even if a cancer is ER-negative, it could still have receptors for HER2, in which case a drug known as Herceptin® could be given, which targets HER2 receptors. If estrogen receptor-negative breast cancer has spread to other areas of the body, a cure is not possible, but treatments such as chemotherapy may be used to control the disease for a length of time, reducing symptoms and improving daily life.