POU1F1 and pituitary tumor: According to the 2017 classification of pituitary tumors by the World Health Organization (WHO), PPA is divided into two subtypes: pituitary transcription factor 1 (PIT-1)-positive plurihormonal pituitary adenomas (PIT-1 + PPA) and plurihormonal adenomas with unusual immunohistochemical combinations (PAwUIC).