With respect to known serum markers, the ratio of patients with a CA19-9 level above the cut-off (≥ 37 U/mL) was significantly higher in the PC group (65%) compared with the control group (5%; P < 0.001), whereas no significant difference was seen between groups with respect to CEA level above the cut-off (≥ 5.0 ng/μL) (10% vs. 30%; P = 0.137). Here, CEACAM5 is linked to pachyonychia congenita.