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. The gene discussed is MUC1; the disease is pachyonychia congenita.