POU1F1 and prolactin-producing pituitary gland adenoma: Intriguingly, we revealed distinct groups as follows: 1) somatotroph adenoma: high POU1F1 and high DLK1; 2) lactotroph adenoma: high POU1F1 and low DLK1; 3) gonadotroph adenoma: high FSHB and low DLK1, followed by high GATA2 and low DLK1; and 4) corticotroph adenoma: high TBX19 and low DLK1.