CD44 and breast cancer: As the growth of BC subtypes is strictly dependent on the activity of several receptors (ErbB family, estrogen, folate, CD44, transferrin receptors), the receptor-mediated drug delivery represents the best therapeutic approach to achieve a selective result following the binding of a ligand–nanoparticle conjugate to the membrane receptors, the nanocarrier internalization through endocytosis, and the drug release via lysosomal degradation to the active sites of tumor cells [66].