Abstract
MicroRNAs (miRNAs) are crucial in the initiation and progression of tumors. A recent study has reported that the miRNAs miR-221 and miR-222 are involved in the promotion of an aggressive basal-like phenotype in breast cancer, functioning downstream of the RAS pathway and triggering epithelial-to-mesenchymal transition. These new insights into the roles of miR-221/222 in breast cancer metastasis, drug resistance and RAS pathways could potentially have applications in medical practice.