Both estrogen receptors (ER) and progesterone receptors (PR) are ligand-activated transcription factors belonging to the family of nuclear hormone receptors. While ER results are the most helpful in predicting therapy response, PR is still an essential marker in breast cancer due to its role in determining the functionality of estrogen receptors in human breast cancer. PR measurements are considered to work as enhancers of the predictive potential of ER test results. The predictive value is significant when assessing pre-menopausal women with primary breast tumors. In immunohistochemical studies, ER and PR receptor staining are localized within the nucleus.
Hormone therapy has been an established therapy for breast cancer treatment for approximately 50 years. Before the development of hormone therapy, the traditional treatment was oophorectomy for pre-menopausal patients and high concentrations of estrogens for other patient groups. These conventional approaches have been replaced mainly with anti-estrogens, aromatase inhibitors, and luteinizing hormone agonists. Research has shown that, overall, tumors reactive to ER and PR regressed, and patient outcomes have improved with hormone therapy.