CD44 and brain neoplasm: The hyaluronic acid (HA) and folate, two general tumor targeting molecules as they have high affinities to CD44 and folate receptors that are highly expressed on various cancer cells including brain tumors, have proven their excellent targeting efficiency of HA or folate-decorated nanomedicines to brain tumors compared to bare nanomedicines (Fig. 3a) [135, 136].