RTN4R and neoplasm: Moreover, targeting may not always be favorable, depending on the carrier: When small polymeric nanoparticles (10 nm) were actively targeted to tumor endothelium by grafting of RGD- or NGR-peptides, they were found to accumulate much more strongly in the tumor tissue than their non-targeted counter parts at early time points, up to 4 h after injection, before the EPR effect became significant.