ER positive refers to a breast cancer that is estrogen receptor‒positive (or ER+), that is, it has receptors for estrogen. This suggests that the cancer cells, similar to normal breast cells, receive signals from the hormone estrogen that could encourage their growth. Approximately 80% of breast cancers are “ER positive,” which means the cancer cells grow in response to estrogen.
About 65% of breast cancers are also PR positive, or progesterone receptor‒positive (or PR+), meaning the cells grow in response to another hormone, progesterone.
When patients receive a breast cancer diagnosis, they are told what type of cancer they have based on the type of tumor, how the tumor may act, and what kind of treatments may work best based on this information. In addition to ER positive, other types of cancer diagnoses include:
- ER/PR positive
- ER/PR negative
For these all of these types of breast cancer, possible treatments include radiation, surgery, and systemic therapies such as chemotherapy, hormone therapies, or other targeted therapy, which are specific to the type of cancer diagnosed. Tumors that are ER positive or PR positive are much more likely to respond to hormone therapy as opposed to tumors that are ER negative and PR negative. Hormone therapy may be given to patients following surgery, chemotherapy, or radiation as well. Such treatments can decrease the potential of the disease recurring.