Estrogen receptor (ER) and progesterone receptor (PR) status

Estrogen receptor (ER) and progesterone receptor (PR) status
Receptors are proteins in or on certain cells that can attach to certain substances, such as
hormones, that circulate in the blood. Normal breast cells and some breast cancer cells
contain receptors that attach to estrogen and progesterone. These 2 hormones often fuel
the growth of breast cancer cells.
An important step in evaluating a breast cancer is to test a portion of the cancer removed
during the biopsy (or surgery) to see if they have estrogen and progesterone receptors.
Cancer cells may contain neither, one, or both of these receptors. Breast cancers that have
estrogen receptors are often referred to as ER-positive (or ER+) cancers, while those
containing progesterone receptors are called PR-positive (or PR+) cancers. If either type
of receptor is present, the cancer is said to be hormone receptor-postive.
Hormone receptor–positive breast cancers tend to grow more slowly and are much more
likely to respond to hormone therapy than breast cancers without these receptors.
All breast cancers, should be tested for these hormone receptors either on the the biopsy
sample or when they are removed with surgery. About 2 of 3 breast cancers have at least
one of these receptors. This percentage is higher in older women than in younger women.