CCDC181 and pachyonychia congenita: However, given the small number of samples in the present analysis, larger studies are needed to examine the association between PC aggressiveness and ctDNA promoter hypermethylation of ST6GALNAC3, ZNF660, CCDC181, and HAPLN3, possibly in combination with the previously identified ctDNA methylation markers suggested to be associated with PC aggressiveness.