NKX6-1 and bile duct papillary neoplasm: To date, 5 TFs have been used as markers for diverse IPN populations: Nkx6.1, Pax7, Otp, Otx2, and Irx2 (Lorente-Cánovas et al., 2012; Moreno-Bravo et al., 2014; García-Guillén et al., 2020).