Ang2 functions as a key regulator of tumor angiogenesis and blood vessel formation in the tumor microenvironment. A fully human anti-Ang2 antibody (3.19.3) was developed to block Ang2 function and showed broad preclinical efficacy in tumor models. Using immunohistochemistry, Brown and colleagues analyzed Colo205 treated tumors following 3.19.3 treatment to visualize tumor associated blood vessels and associated endothelial cells. CD31 stained images (20x), indicated a marked reduction in tumor blood vessel formation and histopathology changes corresponding to areas of increased necrosis, which are hallmarks of anti-angiogenic therapy. For more details, see article by Brown and colleagues on page 145.