RTN4R and neoplasm: For example, the RGD peptide specifically recognises αvβ3 and αvβ5 integrins on tumour endothelia [15], the NGR peptide selectively binds CD13 molecule in tumours but not in other CD13-expressing tissues [20] and the CREKA peptide binds to fibrin-clotted proteins commonly found in sprouting tumour blood vessels [23].