|Fig. 1: Histopathological image of papillary carcinoma (Source; Wikipedia Commons)|
The thyroid gland is a small gland found in the front of the neck composed of two main cells. Follicular cells utilize Iodine from the blood to make thyroid hormones which help to regulate metabolism. C cells, which are also called parafollicular cells, generate calcitonin hormone. Calcitonin governs how the body utilizes calcium. Thyroid cancer can result from the dysregulation of any kind of cell present in the thyroid. There are three types of thyroid cancer: 1) Differentiated, 2) Medullary, and 3) Anaplastic.  Differentiated cancers make up the largest percentage of thyroid cancers and can be further subdivded into papillary cancer (Fig. 1), follicular cancer, and Hurthle cell cancer. Medullary thyroid carcinomas make up a smaller percentage and can be subdivided into sporadic and familial. This type of cancer develops from the C cells of the thyroid gland and can metastasize quickly. Anaplastic thyroid cancer is the most rare type of thyroid cancer and consists of cells that do not look like normal thyroid cells. This cancer spreads quickly and is difficult to treat. 
In general, there is continuing public concern regarding the safety of living nearby nuclear power plants, especially in regards to thyroid cancer risk. This is most likely due to increased cancer incidents following nuclear power plant disasters. For example, the Chernobyl accident in 1986 resulted in a positive correlation between childhood thyroid cancer occurrence and I-131 exposure following the event.  However, following the Fukushima nuclear power plant disaster in 2011, thyroid cancers identified did not show significant links to the radiation exposure from the nuclear power plant. [3,4] Such discrepancies demonstrate a need to further investigate whether or not living near nuclear power plants in general can pose danger to people.
One study suggests that there is no association between living near nuclear power plants and risk of thyroid cancer.  This was achieved by doing a meta-analysis of epidemiological studies that had been performed prior to March 2015. In another study performed in Belgium, scientists also found no increased thyroid cancer incidence in the population that was living approximately 20 km from the nuclear power plants of Doel. 
There are many things to keep in mind when thinking about thyroid cancer incidence in relation to living by a nuclear power plant. Firstly, previous highly publicized disasters may prime the public to have negative reactions about nuclear power plants in general. Next, there is still uncertainty in figuring out quantitatively, if proximity to nuclear power plants can lead to cancer. For example, Mabuchi and Schneider point out that it is difficult to assess these correlations due to the fact that individuals living near such nuclear power plants may be receiving only very small doses of radioactivity. It is difficult to separate the effects of these doses with diet and lifestyle.  Lastly, more sensitive technology and increased cancer screenings may increase thyroid cancer incidence, in general, due to better and more frequent diagnostic tools.  With all this in mind, it is imperative to think twice about assigning correlation to causality when discussing the risks of living near a nuclear power plant.
© Shin-Mei Chan. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
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 K. Mabuchi and A. B. Schneider, "Thyroid Gland: Do Nuclear Power Plants Increase the Risk of Thyroid Cancer?," Nat. Rev. Endocrinol. 10, 385 (2014).
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