The SLC5A5 expression was reduced with the level of the extrathyroidal extension (median values: 5.4 for ‘none’; 2.8 for ‘minimal (T3)’ and 0.9 for ‘moderate/advanced (T4a + b)’), reaching statistical significance for comparisons between ‘none’ vs the ‘moderate/advanced (T4a + b)’ class and ‘minimal (T3)’ vs ‘moderate/advanced (T4a + b)’ (P = 0.018 and P = 0.039, respectively Fig. 2E). We also observed a statistical significant decrease (from a median of 3.8 to 0.8; P = 0.002) of the SLC5A5 expression in cases with new tumor events (Fig. 2F), lumping together 12 cases of distant metastasis (6 lung; 1 lung + bone; 1 lymph node only; 1 lung + femur + neck + pleura + liver; 1 bone; 2 unknown) and 14 locoregional recurrences (10 lymph node only; 2 left thyroid; 1 lymph node + soft tissue; 1 unknown). Finally, SLC5A5 expression was significantly higher in the absence (median = 21.77) of the evaluated mutations: RAS (P = 0.034), TERTp (P = 0.0072) and BRAFV600E (P = 3.1 × 10−8). The PTCs that harbored only TERTp, only BRAF or simultaneous TERTp and BRAF mutations displayed significantly lower expression of SLC5A5 than the WT tumors. The group with RAS mutations displayed the second highest expression value (median = 7.50), reaching statistical significance when compared with the groups including BRAF mutation only and BRAF + TERTp mutations (median = 2.27 in BRAF (P = 0.042); median = 1.89 in TERT+BRAF (P = 0.027)) (Fig. 2G).