The classification recognizes seven main subtypes of pituitary tumors: somatotroph tumors (ST), lactotroph tumors (LT), thyrotroph tumors (TT)—all of Pit-1 lineage—corticotroph tumors (CT, Tpit lineage), gonadotroph tumors (GT, SF-1 lineage), null cell (NC) tumors (no lineage), and plurihormonal tumors (Pit-1 lineage or variable combination of other transcription factors). This evidence concerns the gene POU1F1 and pituitary tumor.