Numerous miRNAs have been shown to have altered expression in a variety of human cancers and function as oncomiRs or tumor suppressors.25–27 For example, constitutive up-regulation of miR-221/222 contributes to poor prognosis in various types of tumors, including hepatocarcinoma, colon, breast, pancreas and lung cancers.12,13,28,29 In breast cancer, miR-221/222 was more abundant in basal-like tumors than in ER/PR–positive tumors14 which in line with our previous findings. Here, ESR1 is linked to cancer.