ESR1 and breast cancer: Overexpression of miR-221 and -222 in ERα-positive breast cancer tissues results in ERα suppression at the post-transcriptional level and also suppresses the expression of different tumor suppressors such as CDKN1B, CDKN1C, BIM, PTEN, TIMP3, DNA-damage-inducible transcript 4, and FOXO3.