CD44 and neoplasm: When doxorubicin-loaded PSiNPs are ingested by tumor cells, they will be sorted and packaged into exosomes, and then secreted by tumor cells into the extracellular space.219 Exosomes-sheathed doxorubicin-loaded PSiNPs have the characteristic of being enriched in the side population cells with features of CSCs, resulting in the elimination of CSCs.219 In addition, Arabi et al.221 used anti-CD44 antibody-encapsulated liposomes to deliver doxorubicin to directly target CD44+ CSCs.