Notably, while MUC1 and MUC16 are transmembrane mucins, their proteolytically cleaved extracellular domains, CA15-3 (a soluble form of MUC1) and CA125 (a soluble epitope of MUC16), serve as soluble biomarkers detectable in the serum of PC patients. Here, MUC16 is linked to pachyonychia congenita.