CCL2 and breast cancer: showed that exosomal miR-200b-3p secreted from breast cancer “educated” alveolar epithelial type II cells (AEC II) to express colony-stimulating factor 1, CCL2, S100A8/9 and MMP9 through AKT/NF-κB/CCL2 cascades by binding to PTEN, thereby creating a suitable microenvironment for MDSC recruitment (88).