Medullary Thyroid Cancer: New Targeted Molecular Therapies

Medullary thyroid carcinoma (MTC) is a rare tumor arising from neural crest-derived parafollicular C cells. Metastatic MTC patients are incurable because the cancer does not respond to radiotherapy or chemotherapy. The elucidation over the past two decades of multiple genetic abnormalities in MTC has provided specific targets for therapy. The identification of activating mutations of the RET tyrosine kinase receptor (TKR) in both hereditary and sporadic MTC makes this malignancy an excellent model to examine the effect of a group of small organic molecule tyrosine kinase inhibitors (TKIs) for treatment of metastatic MTC. Clinical trials with several TKIs targeting RET and other TKRs have shown positive results with generally tolerable toxicity. Approximately one-third to one-half of MTC patients have a reduction in tumor size up to 50%, with the longest treatment duration of approximately four years. The most common treatment-related toxicities are rash, nausea and diarrhea. Despite promising initial results these studies are in their early stages; however, the possibility of testing the sensitivity of primary MTC cells from each subject to different TKIs could increase the effectiveness of the treatment. A brief outline on current patents that are the focus on the treatment of Thyroid Cancer has also been provided in this review.