ULBP2 and pachyonychia congenita: We found that serum CA 19-9 levels were higher in PC patients than in healthy controls (63.4±24.4 versus 28.3±20.2 U/mL, p<0.0001, Fig. 3C); like ULBP2, CA 19-9 levels were not correlated with clinicopathological characteristics (Supporting Table S5).