Emerging Endocrine Therapies in the Treatment of HR-Positive Metastatic Breast Cancer

Breast cancer is the most common malignancy in women worldwide and the most common cause of cancer mortality in women. Seventy percent of breast cancers overexpress the estrogen (ER) and/or the progesterone receptor (PgR) making anti-endocrine therapies the most commonly used worldwide for this disease. These therapies are of low toxicity and low cost since most of them are off-patent and therefore very valuable in the armamentarium against this common form of breast cancer. Selective estrogen receptor modulators (SERMS), selective estrogen receptor down-regulators (SERDS), and aromatase inhibitors (estrogen synthetase) inhibitors (AIs) have been the backbone of recent endocrine treatment of breast cancer. These agents are reviewed here. More recently, combinations of evidence - based targeted therapies with these traditional endocrine therapies have further improved clinical outcomes. In the future, additional agents targeting pathways of resistance to endocrine therapy are likely to be developed.