Medullary Thyroid Cancer: Molecular Biology and Novel Molecular Therapies

Medullary thyroid cancer (MTC) arises from neural-crest-derived parafollicular C cells of the thyroid gland and accounts for approximately 4% of all thyroid cancers. Up to 25-30% of MTC cases occur as inherited disorders while the remaining cases represent the sporadic form of the disease. In this review, the structure and signalling properties of the RET proto-oncogene in its wild-type and mutant forms, and its role in hereditary and sporadic MTC, are discussed. A full data search was performed through PubMed over the years 2000-2008 with the key words 'medullary thyroid cancer, treatment, molecular biology, RET, molecular mechanism', and all relevant publications have been included, together with selected publications prior to that date. We also review novel therapies for metastatic MTC, especially the tyrosine kinase inhibitors which have activity at multiple receptor subtypes, and summarize the current ongoing trials in this area. While such tyrosine kinase inhibitors, particularly those affecting RET activity such as vandetanib, sorafenib and sunitinib, are promising, the low rate of partial responses and absence of complete responses in all of the various trials of monotherapy emphasize the need for new and more effective single agents or combinations of therapeutic agents with acceptable toxicity.