CA 50 is a tumour marker and is similar, but not identical, to the tumour marker CA 19-9.
Carbohydrate antigen 19-9 (CA 19-9) is a modified Lewis(a) blood group antigen.
Mucin occurs in fetal gastric, intestinal and pancreatic epithelia. Low concentrations can also be found in adult tissue in the liver, lungs, and pancreas. CA 19‑9 assay values can assist in the differential diagnosis and monitoring of patients with pancreatic carcinoma. May be used for differentiating patients with cholangiocarcinoma and primary sclerosing cholangitis (PSC) from those with PSC alone.