PLAUR and neoplasm: The mechanisms underlying the retention of uPAR-targeting nanoparticles are multifaceted, as previously discussed by Yang et al. (2009): (i) retention is initiated through active binding of uPAR ligands to uPAR expressed on cancer cells and cancer stromal cells, followed by transcytosis; (ii) uPAR conjugation is essential for enabling nanoparticles to achieve tumor retention.