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(By Leonard Wartofsky, M.D. Reprinted, with permission, from page 17 of Chapter 3 of the reference book “Thyroid Cancer: A Guide for Patients,” (Douglas Van Nostrand, M.D., Gary Bloom, and Leonard Wartofsky, M.D., editors. See http://www.thyca.org/TCGuide.htm)

Are All Thyroid Nodules Cancer?

Most thyroid nodules are in fact benign (non-cancerous), and just the fact that you have a thyroid nodule should not create undue concern that it may be a cancer.

Most nodules rather than being cancer (carcinomas) are actually tumorous collections of benign cells variously called adenomas or adenomatoid nodules.

Whether nodules are "cold" or "hot" on thyroid nuclear scanning relates to their ability to trap and collect radioactive substances such as radioactive iodine or other radioactive elements used in nuclear medicine. These isotopes are either swallowed or injected intravenously and their extraction from the blood and concentration within the nodules causes the areas corresponding to the nodules to show up as black "hot" spots on the scan image.

Hot nodules are rarely cancer and most often represent benign follicular adenomas. In addition, such hot nodules may in fact be overproducing thyroid hormone and may cause hyperthyroidism. The larger the "hot" nodule the more likely it will be associated with hyperthyroidism. These nodules may produce either T4 or T3 or a combination of both.

Approximately 10 to 15 percent of patients with thyroid nodules that can be detected by physical examination will have cancerous nodules.

Most commonly, these cancerous nodules will be a specific type of thyroid cancer derived from the thyroid gland itself; hence they are referred to as primary thyroid tumors.

Less frequently, a nodule may represent spread of cancer from elsewhere in the body (metastatic or "secondary" cancer).