An aqueous tumor-targeting liposome nanoparticle composition comprises an aqueous dispersion of liposome nanoparticles. The nanoparticles preferably encapsulate an anti-cancer chemotherapeutic agent, which can be added to a pre-formed liposome composition or can be incorporated in the liposomes during the formation of the liposomes. The liposome nanoparticles comprise a legumain-targeting lipid admixed with one or more other micelle or vesicle-forming lipid materials in the form of nanoparticulate liposomes dispersed in an aqueous carrier. A preferred tumor-targeting liposome nanoparticle composition comprises a legumain-targeting lipid component and polyethylene glycol-conjugated lipid component. The legumain-targeting lipid component comprising a hydrophobic lipid portion covalently attached to a legumain-binding moiety.