RET and medullary thyroid gland carcinoma: According to the revised American Thyroid Association Guidelines for the management of MTC (hereafter referred to as “ATA-2015”), patients carrying the RET C634 mutation are in the “high risk” (ATA-H) category for developing hereditary aggressive MTC, whereas patients with RET mutations in codons 609, 611, 618, or 620 are in the “moderate risk” (ATA-MOD) category (Table 1, Figure 1) (2).