A drug used to treat medullary thyroid cancer that is locally advanced or has spread to other parts of the body. It is used in patients whose cancer cannot be removed 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. Vandetanib is a type of antiangiogenesis agent and a type of tyrosine kinase inhibitor. Also called Caprelsa and ZD6474.