## 4 Selenium in Thyroid Bland
### Selenium and Thyroid Cancer
Significant increase in production of ROS is observed in thyroid tumor tissue samples vs. healthy tissue [81; 103]. Se is present in high concentrations in the thyroid and plays an important role in the elimination of ROS. Therefore, a fluctuation in its level could affect the expression of antioxidant selenoproteins, sensitive to the intake of Se in the thyroid (GPx1 and GPx3). In the review by [PERSON] et al., studies corroborate the reduction in the activity of selenoproteins in thyroid cancer, in case of Se deficiency [95]. In primary papillary thyroid carcinoma (PTC) samples, reduced or even absent expression of GPx3 has been found in patients and it has been correlated with lymph node metastasis and increased tumor size [112]. In thyroid cancer cell lines TPC-1 and FTC133, GPx3 could inhibit Wnt/\(\beta\)-catenin signaling and thereby suppress metastasis of thyroid cancer [112]. The anticarcinogenic effect of Se during the initiation phase of tumor development is the increased expression of antioxidant selenoproteins. Numerous cohort studies have shown that individuals with plasma selenium levels below 100-120 \(\upmu\)g/L might benefit by increasing their selenium intake. This concentration is the amount needed to reach a \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Analysis** & **Sample** & **Outcome** & **References** \\ \hline Serum Se and & 25 patients with PTC & No significant differences in Se and & \\ GPx3 concentration. & 13 patients with PTC & GPx3 concentrations among groups. & [107] \\ \hline Pre-surgery evaluation of serum & 35 patients with PTC & No significant differences & \\ Se and vit D3 at different stages & 12 patients with PTC & among groups. & [105] \\ of disease. & 17 patients with goiter & No significant association between & \\ \hline Fingermail Se level & 215 patients diagnosed with various thyroid cancer & fingernail Se levels in patients vs & \\  & 331 controls & controls, at different thyroid cancer & \\ \hline Serum concentrations of Se, & Meta-analysis on 1291 subjects & Significantly lower levels of Se and Mn & \\ Cu, Mn & performed in Norwegian, & and higher level of Cu, in patients with thyroid carcinoma & [108] \\ \hline Serum Zn and Se concentration & & Lower serum Se and Zn concentrations & \\ before and after surgery or two & 50 women and men with thyroid cancer & before and after surgery but higher & \\  & & thyroid cancer & concentrations in thyroid tissue in the & \\ thyroid tissues. & & 2 groups & \\ \hline Pre-surgery Se, Cd, Zn serum & & Se, Cd, Zn concentrations were & \\ concentration and correlation to cancer stage & 92 Korean women, of PTC & significantly higher in cancer stages III & [109] \\ \hline Serum and urine concentration & 262 patients with PTC & Se concentrations significantly lower & \\ in eleven metals and in Se & 262 controls & in PTC. & \\  & & Urinary Se concentration negatively & \\  & & associated to PTC risk & \\ \hline GPx1 and TRx1 expression and & 20 samples of thyroid tumor & GPx1 and TRx1 in thyroid cancer tissue & \\ analysis of free radicals tumor & 20 samples of healthy & are lower in patients vs. controls & \\ vs. healthy tissues & 20 samples of healthy & Significant increase in production of & \\  & & thyroid tissue & free radicals in all thyroid tumor tissue \\ \hline Se, GPx3, SePP, Cu, Zn & Patients with various thyroid & \\ serum concentration & pathologies including thyroid & Significantly lower serum Se and Zn & \\  & cancer (n = 323) & levels in patients vs. controls (particular & [10] \\  & 200 Controls & the patients with thyroid malignancy). & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Recent clinical studies conducted on the link between Se and thyroid cancer. plateau in SePP level and beyond, an increase of selenium concentrations no longer provides protective effects on the development of cancer [92]. In cancer cells, abnormal redox regulation is observed at different stage of tumor progression [99]. Tumor cells require antioxidant molecules such as selenoproteins to maintain the redox balance [92].