Blood group related antigens represent a group of carbohydrate determinants carried on both glycolipids and glycoproteins. They are usually mucin-type, and are detected on erythrocytes, certain epithelial cells, and in secretions of certain individuals. Sixteen genetically and biosynthetically distinct but inter-related specificities belong to this group of antigens, including A, B, H, Lewis a, Lewis b, Lewis x, Lewis y, and precursor type 1 chain antigens. Lewis y (type 2 chain) antigen is a difucosylated tetrasaccharide found on the Type 2 blood group oligosaccharides of glycolipids and glycoproteins. It is expressed in large bowel tumors and colorectal carcinomas. It may be useful in the classification of human renal and bladder tumors. The Lewis y antigen has been evaluated as a clinical marker for the diagnosis and prognosis of cholangiocarcinoma, hepatocellular carcinoma and breast cancer.