The abnormal expression of blood group related antigens has been reported in 
many malignant tumours; however, such expression in cholangiocarcinoma has not 
been examined systematically. The expression of blood group-related antigens (A, 
B, H, Lewis(a), Lewis(b), Lewis(x), Lewis(y), carbohydrate antigen 19-9 and 
carcinoembryonic antigen) was investigated immunohistochemically in 75 cases of 
cholangiocarcinoma (31 peripheral type and 44 hilar type). In non-neoplastic 
bile ducts, A, B, and H antigens were expressed in large bile ducts, while 
Lewis(a,b,y) and carbohydrate antigen 19-9 were variably expressed in both large 
and small bile ducts. Lewis(x) and carcinoembryonic antigen was not found in 
non-neoplastic bile ducts. In cholangiocarcinomas, A, B, and H, antigens were 
more frequent in the hilar type than in the peripheral type, although the 
difference was not significant. The expression of the blood-group related 
antigens, particularly A, Lewis(a,b,y), carcinoembryonic antigen, and 
carbohydrate antigen 19-9, was frequent in the tumour cells in well 
differentiated adenocarcinomas, while their immunoreactivity was less frequent 
in poorly differentiated adenocarcinomas. The superanuclear and luminal 
expression of these antigens in carcinoma cells was frequent in well 
differentiated adenocarcinomas, and the diffuse, cell membranous and stromal 
expression of these antigens was relatively frequent in poorly differentiated 
adenocarcinomas and adenosquamous carcinoma. The A, B, and H immunoreactivity of 
both non-neoplastic bile ducts and cholangiocarcinomas was consistent with the 
host blood group type. These findings suggest that both the expression and 
intracellular distribution of blood group-related antigens in cholangiocarcinoma 
are related to the differentiation of cholangiocarcinoma and, possibly, to the 
parent structure.