RB1 and pachyonychia congenita: The immunohistochemical profile of PC was investigated by stains for parathyroid cell marker parathormone, chromogranin A, and GATA3, as well as parafibromin, E-cadherin, galectin-3, PGP9.5, p53, retinoblastoma protein (pRb), and Ki-67 [5,7,14].