TP53 and pituitary gland adenoma: Although “atypical adenoma” was defined by the WHO in 2004 as “increased fission, Ki-67 labeling index > 3%, and positive p53 immunostaining, not all tumors that meet the criteria show an aggressive course, and even ordinary pituitary adenomas may meet the criteria; thus, “atypical adenoma” was deleted in the 4th edition of the WHO classification [17].