Prepared by Dr. Pedram Argani, lead pathologist for breast cancer at Johns Hopkins.

The estrogen receptor is present in normal breast epithelium, where it mediates cell proliferation (growth) in response to hormonal changes in the menstrual cycle. Estrogen receptor is present in approximately two-thirds of invasive breast carcinomas, where is presumably mediates hormonally driven tumor growth. In other words, the normal estrogen in the body stimulates the tumor to grow, just as it stimulates the normal breast epithelium to grow. The presence of estrogen receptor in invasive carcinoma is a favorable prognostic factor, since outcome is slightly better regardless of the therapy given. More importantly, the presence of estrogen receptor in invasive carcinoma is an important predictive factor of response to endocrine therapy; specifically, Tamoxifen. In general, estrogen receptor positive tumors respond, estrogen receptor negative tumors do not