Tumors induce the formation of new blood vessels through a process called angiogenesis. However, these new vessels are often abnormal, with large gaps between endothelial cells. This increased vascular permeability allows macromolecules and nanoparticles to pass through and accumulate in the tumor tissue. Additionally, tumors often have impaired lymphatic drainage, which leads to the retention of these therapeutic agents within the tumor microenvironment.
