Treatment of ER-positive breast cancer with FDA-approved aromatase inhibitors

Breast cancer is a leading cause of death among women globally. Estrogen receptor (ER)-positive breast cancers account for ∼70 % of breast cancer diagnoses worldwide. Endocrine therapy is the primary treatment approach for ER-positive breast cancer. In the United States, the Food and Drug Administration (FDA) has approved several endocrine therapies for ER-positive breast cancers, including selective estrogen receptor modulators (SERMs), selective estrogen receptor downregulators/degraders (SERDs), and aromatase inhibitors (AIs). The current FDA-approved SERMs include tamoxifen, toremifene, and raloxifene, while the only SERD that has been approved to date is fulvestrant. Various generations of AIs are available for the treatment of hormone-positive breast cancers, including exemestane, letrozole, and anastrozole. Aromatase inhibitors are often utilized following relapse with therapies such as tamoxifen. Herein, we focus on and review the major FDA-approved aromatase inhibitors used to treat ER-positive breast cancer.