What does it mean to have an oestrogen receptor positive or oestrogen receptor negative breast cancer?
For over 100 years doctors have known that reducing the level of the female hormone, oestrogen, can cause some breast cancers to get smaller. In the late 1960s scientists discovered a group of proteins in breast cancer cells that could take up oestrogen from the blood stream and use it to help the cells grow and multiply. They called these proteins oestrogen receptors (now usually abbreviated to ER). It was also shown that the breast cancers that shrank when oestrogen levels were reduced, contained oestrogen receptors (ER). By contrast, those tumours that were unaffected by lowering oestrogen in the body had little or no ER. Nowadays most breast cancers are routinely tested in the laboratory to see whether or not they contain ER. Those cancers which do have the receptors are called oestrogen receptor-positive (ER+ve) and those that don’t are called oestrogen receptor-negative (ER-ve). Sometimes tumours contain only small amounts of ER and these are labelled as being weakly positive. Kn
