Estrogen receptors are found in cancer cells. Cancers that contain Estrogen Receptors are known as ER positive. These receptors use the hormones in your body as the aids to grow. The Estrogen receptors are mostly found in breast cancer cells. The cancers with these receptors are known as hormone responsive cancers. In order to detect these cancers and their stage, it is very important that this test be done as soon as the symptoms are seen. IHC or Immunohistochemistry is used to check whether the cancer cells contain receptors on their surface or not. This plays seminal role in deciding the course of medications.