GDF15 and thyroid cancer: Since mature NAG-1 has been detected in the antibody array and mature serum NAG-1 is linked to thyroid pro-tumorigenesis [28], we measured serum NAG-1 levels to identify the linkage in different types of thyroid cancer: non-aggressive benign thyroid nodules (BTN: FA and NH) and aggressive differentiated thyroid cancer (DTC: FVPTC, PTC, and FTC).