RET and endocrine system disorder: Considering MTC aggressiveness and the co-existing endocrinopathies such as pheochromocytoma (PHEO), hyperparathyroidoism (HPTH), cutaneous lichen amyloidosis (CLA), and Hirschsprung’s disease (HD), the American Thyroid Association (ATA) Guidelines currently divide germline RET mutations into three risk categories: ATA–HST (the highest risk—patients with MEN2B and the RET codon M918T mutation), ATA-H (the high risk—patients with RET codon C634 mutations and the RET codon A883F mutation), and ATA-MOD (moderate risk—patients with all other mutations in the RET gene) [9].