Furthermore, in hormone receptor-positive BC cells resistant to endocrine therapy (tamoxifen), the miR-221/222 cluster is upregulated through the negative regulation of cyclin-dependent kinase inhibitor 1B (p27Kip1) (Hanna et al., 2012; Gan et al., 2014; Miller et al., 2008). This evidence concerns the gene CDKN1B and breast cancer.