EGFR and neoplasm: Quantitative biodistribution analyses using fluorescence resonance energy transfer (FRET) reveal that active targeting shifts accumulation from 5–10% passive to 15–25% active in tumor tissues, with reduced off-target in liver (from 40% to 20% of dose), as seen in anti-EGFR cetuximab-nanoparticles for glioblastoma, where blood-brain barrier crossing is facilitated by transferrin receptor shuttling, achieving 2–3-fold higher glioma penetration [19].