PGP and osteosarcoma: EVs carrying P-glycoprotein (P-gp, MDR-1 or ABCB1), one of the most well-studied drug efflux pump, have been implicated in the transfer of multidrug resistance to sensitive cells in several human cancer models, such as prostate and ovarian cancers, acute T lymphoblastic leukemia, and osteosarcoma [97–100].