Among NENs, the most frequent sources of ectopic ACTH production are lung carcinoids (>25%), followed by thymic carcinoids (TC, 11–25%, including cases associated with Multiple Endocrine Neoplasia type 1, MEN-1), pancreatic neuroendocrine tumors (8%), medullary thyroid carcinomas (MTC, 6%), and pheochromocytomas (5%) (7–9). This evidence concerns the gene POMC and medullary thyroid gland carcinoma.