POMC and neoplasm: The source of ACTH hypersecretion in ACTH-immunoreactive forms of MPA is mainly eutopic due to hyperfunctional pituitary corticotroph adenoma cells; however, ACTH may also derive from ectopic corticotroph tumor cells located in the parasellar area, the neurohypohysis, or the pituitary stalk (30, 67).