Vandetanib is primarily used in the treatment of medullary thyroid cancer, particularly in cases where the cancer is advanced, inoperable, or has spread to other parts of the body. It works by inhibiting specific tyrosine kinase enzymes that are involved in the growth and spread of cancer cells. This targeted approach helps to slow down or stop the progression of the disease. Additionally, vandetanib may be considered for patients who are not candidates for surgery or other localized treatments. It is administered orally, making it a convenient option for long-term management of the condition. Regular monitoring is essential during treatment to manage potential side effects and ensure its effectiveness.