Thyroid cancer is the most common malignancy of the endocrine system. Medullary thyroid cancer (MTC), an intermediate differentiated histotype of thyroid cancer, accounts for approximately 4% of all thyroid cancer cases in the United States. MTC tumors are characterized by increased activation of the proto-oncogene RET, which encodes a receptor tyrosine kinase that promotes cell growth, differentiation, and survival. RET mutations are present in almost all patients with hereditary MTC and in up to 50% of patients with sporadic MTC. MTC tumors also are characterized by overexpression of vascular endothelial growth factor receptors. Until recently, systemic therapy options for MTC treatment were limited. However, based on promising efficacy demonstrated in other solid tumor types, many oral tyrosine kinase inhibitors are being investigated for the treatment of patients with MTC. Recently, vandetanib was approved in the United States for the treatment of patients with symptomatic or progressive MTC with locally advanced or metastatic disease. Common adverse events associated with tyrosine kinase inhibitors under investigation for MTC include diarrhea, rash, hypertension, and QTc prolongation.
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