For example, in pancreatic ductal adenocarcinoma (PDAC), spatial variations in CA19-9 and CD175 (Tn antigen) expression have been observed: CA19-9 is predominantly expressed on O-glycans, while CD15s (sialyl-Lewis X) localizes to both N-glycans and O-glycans [35]. The gene discussed is FUT4; the disease is pancreatic ductal adenocarcinoma.