Figure 1.

Schematic representation of enhanced permeability and retention (EPR) effect. Typical blood vessels from solid tumors contain pores of various sizes that allow the nanoparticles (NPs) and molecules of the drug to enter the interstitium of the tumor tissue. A, The free chemotherapeutic drugs are small in size and reach the tumor site through free diffusion. Only a small amount of drug can reach the tumor site. There is no significant difference in drug concentration between tumor tissues and other healthy tissues. B, The size of the NPs allows them to penetrate the extravascular space through the gap and accumulate inside the tumor, where the carrier releases the drug.⁴¹