Tissue expression of the tumour associated antigen CA242 in benign and malignant pancreatic lesions. A comparison with CA 50 and CA 19-9.

The expression of a novel tumour associated antigen CA 242, defined by the monoclonal antibody C 242, was studied by immunoperoxidase staining in formalin-fixed, paraffin-embedded tissue sections from normal pancreata, pancreata with pancreatitis and benign and malignant pancreatic neoplasms. The antigenic determinant of the C 242 antibody is a sialylated carbohydrate structure, related but chemically different from tumour marker antigens CA 19-9 and CA 50. Thirty-eight of 41 (93%) well to moderately differentiated ductal adenocarcinomas of the pancreas and all cystadenocarcinomas were positive for CA 242. The staining was most intense in the apical border of the cells, and in the intraluminal mucus. Only two out of seven poorly differentiated adenocarcinomas stained, and the number of positive cells was smaller than in well differentiated carcinomas. Only occasional cells were stained in one out of five anaplastic carcinomas. Part of large ducts were positive in 91% (21/23) specimens of chronic pancreatitis. In acute pancreatitis small terminal ducts, centro-acinar cells and some large ducts stained for CA 242. In normal pancreas only a few small terminal ducts were CA 242 positive. Carcinomas always stained more strongly for CA 242 than normal pancreatic tissue adjacent to the carcinoma. The results of CA 242 are compared with those of tumour marker antigens CA 50 and CA 19-9. Serum CA 242 levels were determined in 23 of the patients with pancreatic cancer using a fluoroimmunoassay. Fifteen (65%) patients had an elevated value. There was no clear-cut correlation between the serum levels and the immunohistochemical expression of the CA 242 antigen. The expression of CA 242 in pancreatic tissue resembles that of CA 50 and is similar to CA 19-9. The antigen is expressed in serum of many patients with pancreatic cancer and, therefore, is a potential candidate for a serum tumour marker.