ABSTRACT
The discovery of estrogen and progesterone receptors (ER/PR), the direct role of estrogen on breast cancer growth and its relation to ER were recognized by late 1960s. While this chapter focuses on aromatase inhibitors; it is worth mentioning that apart from anti-estrogens and methods to achieve estrogen deprivation, there is evidence showing effectiveness of other endocrine treatment modalities. The first reported case of endocrine therapy was in form of oophorectomy in 1895. In addition to refining biomarkers to predict hormone sensitivity, both overall and specific to different endocrine agents, pharmacogenomics has become important with a potential to “personalize” endocrine therapy for breast cancer. By late 1960s the direct role of estrogen on breast cancer growth and its relation to ER was described. Endocrine treatment modalities broadly operate by acting as an anti-estrogen interfering with the binding between estradiol and ER, or by depriving circulating estradiol.
