POMC and neoplasm: In AtT-20 pituitary ACTH-secreting tumor cells, an experimental cellular model of corticotroph adenomas, RA inhibits POMC transcription and stimulation of POMC by corticotropin-releasing hormone (CRH), being these effects highly specific because RA does not affect key factors of the corticotroph function such as cAMP response element-binding, GR, and paired-like homeodomain X 1 (112).