COL6A6 and cholangiocarcinoma: In urine, peptide markers are derived from the following proteins with well-described associations to CCA pathology in literature: KNG1, FXYD2, α-1-antitrypsin (SERPINA1), interleukin-1 receptor accessory protein-like 1 (IL1RAPL1), CD99 antigen, SPP1 and the collagen chains COL1A1, COL17A1, COL1A2, COL2A1, COL5A2 and COL6A6.