TFRC and central nervous system cancer: Furthermore, even with targeted delivery approaches using functionalized NPs that preferentially recognize protein receptors on cell surfaces (i.e., transferrin receptors on the surfaces of glioma cells), the percent injected dose of NPs that ultimately cross the BBB via the bloodstream is meager and would require dosing human subjects with hundreds of milliliters of NPs intravenously to achieve a detectable phenotypic effect (Wilhelm et al., 2016).