MUC1 and carcinoma: We tried to further classify ACs into 3 subtypes on the basis of the expression of CK20 and MUC1 in the intestinal mucosa and the pancreatobiliary mucosa: tumors expressing CK20 and lacking MUC1 were defined as intestinal type (I-type); tumors expressing MUC1 and lacking CK20 were defined as pancreatobiliary type (PB-type); and carcinomas expressing or lacking both CK20 and MUC1 were defined as other type (O-type).