CD9 and neoplasm: In addition, EVs also play a key role in mediating tumor drug resistance.122,123 Many studies have reported that the delivery of EVs secreted by drug-resistant tumor cells to sensitize tumor cells enhances the drug resistance of the latter.13,122,124 Drug-resistant tumor cells usually overexpress a variety of proteins related to drug efflux, including ABCG2, P-gp, ABCA3, and MRP1.