Finally, a small study examining 15 post-menopausal, ER+ breast cancer patients receiving Exemestane (an AI) and Tamoxifen for 4 months prior to surgery found up-regulation of a panel of miRNAs after treatment (miR-21, miR181b, miR-26a/26b, miR-27b and miR-23b), providing insight into the effect of Exemestane and Tamoxifen on miRNA expression [17]. This evidence concerns the gene ESR1 and breast cancer.