PTEN and breast cancer: miR-222 is transferred in EVs between drug-resistant and sensitive tumour cells, conferring resistance to common BC drugs including tamoxifen, docetaxel and adriamycin by downregulating ERα and PTEN in recipient cells [128–130], and EV-mediated transfer of miR-222 and miR-223 from MSCs to BC cells in the bone marrow induces BC cell dormancy, promoting quiescence and resistance to carboplatin in metastatic cells prior to recurrence [131].