For instance, octreotide is partially effective in patients with extra-pituitary corticotroph tumors responsible for ectopic Cushing syndrome or ectopic ACTH secretion and is generally ineffective in patients with pituitary corticotroph tumors responsible for the most common form of ACTH-dependent Cushing syndrome, namely, Cushing disease (17, 18). This evidence concerns the gene POMC and Cushing syndrome.