On these premises, the aims of the present single-center, retrospective study were: (1) the clinical, pathological and molecular characterization (based on BRAF, RAS, TP53, PTEN, PIK3CA genes, and TERT promoter analysis) of selected cases of DTC with or without distant metastases, grouped by primary tumor size: group 1 included patients with tumors ≤ 40 mm in size and no distant metastases; group 2 included patients with tumors > 40 mm in size, with no distant metastases; and group 3 included patients with metastatic DTC, regardless of tumor size. This evidence concerns the gene TERT and neoplasm.