XBP1 and pachyonychia congenita: Given that CP was regarded as a high risk factor for PC, in the present study, we aimed at characterizing the expression of ER stress-related proteins ATF6/XBP1/CHOP/EMC6 and apoptosis-related protein APAF1 in PC, and at analyzing the relationship between their expression, the clinico-pathological variables, and prognosis of surgically resected PC patients.