The pathogenesis of transformation of corticotroph adenomas from the silent type to the functional type is still unclear, but it was speculated that the biological activity of ACTH decreased in SCAs, which led to the fact that, although ACTH was IHC positive, the efficacy was not enough to cause biochemical and clinical symptoms of Cushing's syndrome (26). This evidence concerns the gene POMC and ACTH-producing pituitary gland adenoma.