A defining characteristic of tumor-penetrating peptides and many of the natural ligands of NRP-1 (e.g., VEGFA165, Semaphorin-3) is that their specific interaction with NRP-1 is conditional and dependent on the C-terminal exposure of the R/KXXR/K motif, leading to its designation as the C-end Rule (CendR) motif [18–20]. Here, NRP1 is linked to neoplasm.