Estrogen Receptor Test for Breast Cancer - Immunohistochemistry: Estrogen Receptor (ER)

Immunohistochemical (IHC) testing for estrogen receptor (ER) aims to detect the presence of ER proteins within the nuclei of cancer cells in breast tissue and other tissues. The result of this test (positive or negative) determines whether the breast cancer is "hormone-dependent" and, consequently, its responsiveness to anti-estrogen hormonal therapies such as tamoxifen or aromatase inhibitors.