Letrozole improves the sensitivity of breast cancer cells overexpressing aromatase to cisplatin via down-regulation of FEN1

Purpose Flap endonuclease 1 (FEN1) is up-regulated by estrogen (17β-estradiol, E2) and related to cisplatin resistance of human breast cancer cells. Letrozole, an aromatase inhibitor, suppresses the change of testosterone into estrogen and is frequently used to treat breast cancer. However, the effects of letrozole on FEN1 expression and cisplatin sensitivity in breast cancer cells overexpressing aromatase have not been revealed.