KRT18 and extramammary Paget disease: Since IHC for p40, B72.3, p53, programmed death-ligand 1 (PD-L1), and RANKL was only performed on primary EMPD and IHC for CK8, CK18, CK19, MUC5AC, p16, MUC6, pan-keratin, progesterone receptor (PR), thrombomodulin, and Wilm’s tumor 1 (WT1) were only performed on secondary EMPD; the diagnostic role of these stains in distinguishing primary versus secondary EMPD cannot be evaluated (Table 3).