Definition of Cancer, thyroid

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Cancer, thyroid: A malignant tumor of the gland in front of the neck that normally produces thyroid hormone, which is important to the normal regulation of the metabolism in the body. There are four major types of cancer of the thyroid gland: papillary, follicular, medullary, and anaplastic. Persons who received radiation to the head or neck in childhood should be examined by a physician for thyroid cancer every 1 to 2 years. The most common symptom of thyroid cancer is a lump, or nodule, that can be felt in the neck. The only certain way to tell whether a thyroid lump is cancer is by examining thyroid tissue obtained via biopsy.