UPK2 and extramammary Paget disease: Conventional IHC panels including keratin 7 (CK7), keratin 20 (CK20), gross cystic disease fluid protein 15 (GCDFP15), caudal-type homeobox 2 (CDX2), uroplakin II/III and GATA binding protein 3 (GATA3) are routinely employed to distinguish primary and secondary EMPD; however, overlapping immunoprofiles can complicate interpretation and contribute to diagnostic uncertainty [3,5,8].