CD63 and breast carcinoma: Recently, Gao et al. identified and characterized a subtype of CAFs which particularly has the presence of the cell surface protein CD63; these CD63+ CAFs are capable of secreting exosomes enriched in miR-22, which can bind to their targets, ERα and PTEN, and deregulate their expression, thus conferring tamoxifen resistance to breast cancer cells (Gao et al., 2020).