NRP1 and neoplasm: Briefly, iRGD exerts its function following 3 key steps: (1) iRGD peptides bind to integrins (αvβ3 and αvβ5); (2) the peptide is proteolytically cleaved in tumors to produce CRGDK/R and expose the activated CendR motif (R/KXXR/K) at the C-terminus; and (3) CendR binds to NRP-1 to trigger tumor tissue penetration (Figure 1).