Estrogen and progesterone receptor (ER/PR) tests identify whether these
hormones affect the way that breast cancer grows. The results of these tests help doctors decide whether to use hormone therapy to help stop the cancer from
growing or to lower the risk of the cancer coming back (recurrence).
The hormones estrogen and
progesterone attach to certain receptors on the breast cells to stimulate the growth of normal breast cells and some
Breast cancer cells that lack these
receptors (ER-negative and PR-negative cancers) are much less likely to respond
to treatment with such medicines as tamoxifen or aromatase inhibitors.
ER/PR-positive tumors have these receptors and are more likely to respond to
treatment with tamoxifen or aromatase inhibitors.