Estrogen receptor alpha (ESR1) - Marker for female tissues and cancers

The estrogen receptor alpha (ER) is a transcription factor that is activated upon the binding of the hormone estrogen, and is important for sexual development and reproductive function in females. The estrogen receptor is expressed by all female tissues (e.g. breast, vagina, uterus and cervix) and clinically; ER is used as a marker to diagnose cancers originating from these tissues. Moreover, together with the progesterone receptor, the estrogen receptor is also used as a predictive biomarker since tumors that are estrogen-/progesterone receptor positive are also susceptible to hormone-blocking drugs.