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Summary: The expression of six sialylated carbohydrate antigens (CA19-9, CA-SO, SLEX, SLX, DU-PAN-2, ST-439) was examined in malignant and nonmalignant pancreatic tissues using an immunohistochemical method to elucidate the characteristics of these carbohydrate antigens as tumor markers. All carbohydrate antigens except for sialyl SSEA-I (SLX, 52.4%) were expressed in more than 80% of the pancreatic cancer. CA19-9 and CA-50, belonging to type I blood group antigens, and DU-PAN-2 and ST-439 were localized predominantly in the cytoplasm of cancer cells, while sialyl Lex (SLEX) and SLX, belonging to type II blood group antigens, were stained mainly on the apical membranes of malignant glands. Although type I antigens were expressed in most nonmalignant pancreatic tissues, the type II antigens and ST-439 were absent in almost all of the normal tissues and faintly expressed in few chronic pancreatitis tissues, suggesting the high tumor specificity of these antigens. Each antigen was expressed on the apical surface of ducts in normal pancreas. However, in about 30% of chronic pancreatitis cases, type I antigens and DU-PAN-2 were observed in the cytoplasm of ductal cells. All patients showing stromal stain, possibly caused by loss of antigen polar expression and shedding into the surrounding stroma adjacent to malignant glands, revealed high levels of serum antigen. This finding suggests that the stromal appearance of antigens is a significant factor in the elevation of serum antigen levels.

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