POMC and adenoma: Adrenocorticotropin (ACTH) is widely used as a marker of hormonally active adenoma or, less commonly, carcinoma of the pars intermedia of the pituitary gland in horses, which causes a clinical syndrome called pituitary pars intermedia dysfunction (PPID) (Equine Endocrinology Group, 2021; Heinrichs et al., 1990; Love, 1993).