The importance of steroid hormone receptors to the biology of breast cancer was recognized over 40 years ago, when it was observed that radiolabeled estrogens concentrated preferentially in the estrogen-influenced target organs of both animal and human breast cancers. These findings gave rise to the concept of an estrogen receptor (ER). It has since become clear that human breast cancers are dependent upon estrogen and/or progesterone for growth and that this effect is mediated through ERs and progesterone receptors (PRs). Not surprisingly, ERs and PRs are both overexpressed in malignant breast tissue.
New insights into hormone receptor biology and the increasing array of proteins that can modify their function have already translated into better therapies for breast cancer. As an example, a number of drugs that interact with the receptor, including selective ER modulators (SERMs) and selective ER downregulators (SERDs), are approved for the treatment and prevention of breast cancer. At the same time, improved methods for assaying receptor proteins have led to less expensive and simpler measurements of ER and PR. Unfortunately, however, these methods have been fraught with variation that has resulted in inaccurate test results. Since these tests guide the use of endocrine therapy in patients with breast cancer, the American Society of Clinical Oncology (ASCO) and the College of American Pathologists (CAP) convened a panel to address causes of variation related to measurement of ER and PR by immunohistochemistry (IHC) in 2010 [1,2].
Here we review the clinical utility of hormone receptor testing in breast cancer and the guideline recommendations published in 2010 for measurement of ER and PR in tissue samples by IHC. An overview of ER biology, the mechanism of action of SERMs at the level of the hormone receptor, the use of endocrine therapy for adjuvant treatment of early stage breast cancer and for treatment of metastatic disease, and an overview of prognostic factors for patients with breast cancer are discussed elsewhere.
●(See "Molecular biology and physiology of estrogen action".)
●(See "Mechanisms of action of selective estrogen receptor modulators".)