Drug resistance is another issue with MSC-exosomes; in particular, those containing miRNA-222/223 or miRNA-23b make breast cancer resistant to the proteasome inhibitor docetaxel, and BMSC-exosomes carrying upregulated mRNAs of PSMA3 and PSMA3-AS1 drug transporter proteins may cause resistance in multiple myeloma cells [230]. This evidence concerns the gene PSMA3 and breast cancer.