Estrogen receptors (ER) and progesterone receptors (PR) are normally found in the tissues where their respective target hormones play a regulatory role, such as the uterus, pituitary gland, hypothalamus, and breast. Upon hormone binding, the respective receptors form a large protein complex that activates transcription. As these receptors are tissue-based, the determination of their presence or absence requires a representative tissue sampling.
Both ER and PR are used in breast cancer as indicators for hormonal therapy. Those positive for ER and PR will typically respond to hormonal treatment, while those with negative receptors will require other treatment modalities, such as chemotherapy.2
Patients with positive ER and PR typically are associated with a better prognosis and higher survival rate.