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. Caprelsa 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 vandetanib and ZD6474.