CD44 and neoplasm: Several factors likely underlie the performance of DOX/HA-b-PCDA NPs: (1) prolonged circulation and EPR effect enhance tumor accumulation; (2) HA-mediated active targeting increases cancer cell uptake; (3) small size facilitates penetration into tumor tissue; (4) the binding of HA and CD44 enables access to chemoresistant BCSCs; (5) dual cytotoxic effects against both differentiated tumor cells and BCSCs.