For more than 100 years, hormonal therapy has been known to be effective in the treatment of
breast cancer. Initially, this therapy was dominated by the selective
estrogen receptor antagonists such as
tamoxifen.
Aromatase inhibitors (AIs) are a distinct drug class with demonstrated activity in the treatment of
hormone-sensitive
breast cancer. All 3 third-generation AIs,
exemestane,
anastrozole, and
letrozole, have been studied in multiple lines of therapy in advanced
breast cancer and have demonstrated equivalence or superiority compared with
tamoxifen. While initially developed as a treatment option for advanced disease, the AIs have also shown efficacy in the treatment of curable disease, including the neoadjuvant and adjuvant settings. In addition, the AIs demonstrate a tolerable side effect profile in comparison with
tamoxifen, and this has led to their early incorporation as standard of care therapy. Given the proven efficacy of AIs across the spectrum of
breast cancer, the remaining questions include definitive sequencing strategy, timing, and duration of use. Ongoing trials include head-to-head comparisons between the AIs in early-stage
breast cancer; the results of these trials are eagerly anticipated and should further optimize the use of AIs.