The Medullary Thyroid Carcinoma (MTC) Registry Consortium* is partnering with the American Thyroid Association® (ATA) to create a registry (list) of adult (18 years of age and older) cases of MTC diagnosed in the United States in order to characterize their medical histories and possible risk factors, including history of treatment with long-acting GLP-1 RAs from January 1, 2010 to present (the MTC Registry).