Estrogen and progesterone receptor (ER/PR) tests

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 cancers.

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.

The Health Encyclopedia contains general health information. Not all treatments or services described are covered benefits for Kaiser Permanente members or offered as services by Kaiser Permanente. For a list of covered benefits, please refer to your Evidence of Coverage or Summary Plan Description. For recommended treatments, please consult with your health care provider.