Tissue distribution of 2‐3 and 2‐6 sialyl lewis A antigens and significance of the ratio of two antigens for the differential diagnosis of malignant and benign disorders of the digestive tract

The authors investigated the tissue distribution of two kinds of sialylated derivatives of Lewis A (Lea) antigen in patients with cancers of the digestive system using specific monoclonal antibodies, and evaluated the significance of determining the 2‐3 and 2‐6 sialylated Lea antigen levels for the diagnosis of cancer. In most specimens from patients with cancers of the pancreas, biliary tract, stomach, and colon, the 2‐3 sialylated Lea antigen was strongly expressed in cancer cells. However, 2‐6 sialylated Lea antigen was less frequently expressed in cancer cells. The former is therefore more specific to cancer than the latter. Also, the serum level of the 2‐3 sialylated Lea antigen was significantly higher than that of the 2‐6 counterpart in patients with cancers of pancreas, biliary tract, stomach, and colon. The resulting ratio of serum 2‐3/2‐6 sialylated Lea antigens was frequently high in patients with malignancy and was low in patients with benign disorders of these digestive organs. Therefore, the 2‐3/2‐6 sialylated Lea antigen ratio is a useful for the differential diagnosis of malignant disorders in these organs. However, liver disorders were found to be exceptional in that both antigens were mostly absent in hepatocellular carcinoma (HCC) cells in immunohistologic examination, as well as in nonmalignant parenchymal liver cells. Only the epithelial cells of the intrahepatic bile ducts expressed the 2‐6 sialylated Lea antigen strongly, and expressed the 2‐3 sialylated Lea antigen moderately. The levels of both antigens were sometimes high in patients with liver disorders, but the ratio always remained low in patients with HCC as well as benign liver disorders such as cirrhosis or chronic hepatitis. The sialylated Lea antigens, which sometimes accumulate in the sera of patients with HCC, were concluded to originate from the epithelial cells of the proliferating small bile ducts, and those serum antigens cannot be considered as evidence for the presence of liver cancer cells.