Estrogen Receptor Assay

The ER or estrogen receptor assay is a test done on fresh tissue obtained from the breast to see if a tumor is likely to respond to endocrine (hormonal) therapy. It is done under a microscope to determine the predicted outcome of breast cancer and also how well the cancer will respond to hormone therapy. Tumors with a positive ER assay are much more likely to respond to hormone therapy than tumors that have a negative ER assay.

In addition to breast tumors it is often performed also on specimens of endometrial tumors (cancer of the uterus), adenocarcinomas, and metastatic carcinoma (tumors which have spread from the area in which they started). Often a progesterone receptor assay will be included with the ER. Together, the (PR & ER) are more helpful in determining the prognosis and treatment needed than alone.


All hormone use and anti-estrogen preparations should be stopped two months prior to biopsy as this may show up as a lower receptor level.


Negative: Less than 5% of the cells stain for receptors

Positive: Greater than 5% of the cells stain for receptors

Ranges for normal findings may vary among different laboratories and hospitals. You should always check with your doctor after having lab work or other tests done to discuss the meaning of your test results and whether your values are considered within normal limits.


Your caregiver will go over the test results with you and discuss the importance and meaning of your results, as well as treatment options and the need for additional tests if necessary.


It is your responsibility to obtain your test results. Ask the lab or department performing the test when and how you will get your results.