What causes thyroid cancer?

Updated: May 14, 2020
  • Author: Pramod K Sharma, MD; Chief Editor: Arlen D Meyers, MD, MBA  more...
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Thyroid carcinomas arise from the 2 cell types present in the thyroid gland. The endodermally derived follicular cell gives rise to papillary, follicular, and probably anaplastic carcinomas. The neuroendocrine-derived calcitonin-producing C cell gives rise to MTCs. Thyroid lymphomas arise from intrathyroid lymphoid tissue, whereas sarcomas likely arise from connective tissue in the thyroid gland.

Radiation exposure significantly increases the risk for thyroid malignancies, particularly papillary thyroid carcinoma. This finding was observed in children exposed to radiation after the nuclear bombings in Hiroshima and Nagasaki during World War II. Additional evidence was gathered after atomic bombs were tested in the Marshall Islands, after the accident at the Chernobyl nuclear power plant, and in patients who received low-dose radiation therapy for benign disorders (eg, acne, adenotonsillar hypertrophy). Low-dose radiation exposure from imaging studies has not been found to have a tumorigenic effect. Radiation targeting the thyroid gland (eg, iodine-131 ablation of the thyroid) or high-dose external-beam radiation therapy does not appear to increase the risk of papillary thyroid carcinoma. This is presumably because cell killing increases with these doses.

A study by Le et al indicated that among patients in the Veterans Health Administration (VHA) with thyroid cancer, the percentage of those with self-reported exposure to Agent Orange is significantly higher than in the general VHA population. The study included 19,592 patients diagnosed with thyroid cancer. [9]

Low dietary intake of iodine does not increase the incidence of thyroid cancers overall. However, populations with low dietary iodine intake have a high proportion of follicular and anaplastic carcinomas.

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