An orally bioavailable 4-anilinoquinazoline. Vandetanib selectively inhibits the tyrosine kinase activity of vascular endothelial growth factor receptor 2 (VEGFR2), thereby blocking VEGF-stimulated endothelial cell proliferation and migration and reducing tumor vessel permeability. This agent also blocks the tyrosine kinase activity of epidermal growth factor receptor (EGFR), a receptor tyrosine kinase that mediates tumor cell proliferation and migration and angiogenesis. OR A drug used to treat medullary thyroid cancer that has spread to other parts of the body and cannot be treated by surgery. It is also being studied in the treatment of other types of cancer. Vandetanib prevents the growth of new blood vessels that tumors need to grow. It also blocks enzymes needed for cell growth and may kill cancer cells. It is a type of antiangiogenesis agent and a type of tyrosine kinase inhibitor. Also called Caprelsa and ZD6474.