Tumour markers CA 19-9 and CA 50 in digestive tract malignancies.

CA 19-9 and CA 50 are tumour marker tests measuring the same carbohydrate structure, sialosyl-fucosyl-lactotetraose--that is, the sialylated Lewis blood group antigen. In addition, the C50 antibody reacts with sialosyl-lactotetraose, which may be expressed in small amounts in some carcinomas. In this study we compared these tests in sera from patients with benign and malignant digestive tract diseases. The sensitivity of the markers for different cancers was also compared at several specificity levels with patients with benign diseases as reference groups. Both markers showed a high sensitivity for pancreatic cancer (77% for CA 19-9; 69% for CA 50) and biliary cancer (88%). The figures in colorectal cancer were almost as high as those reported for CEA; 16-21% elevated values in Dukes A and B tumours and 44-47% in Dukes C and D tumours. The sensitivity for gastric cancer was 48% for both markers. CA 50 had a higher sensitivity for liver cancer (55%) than CA 19-9 (9%), but the proportion of elevated values in benign liver diseases was also higher (33% versus 15%, respectively). Overall, there was good correlation between the CA 19-9 and CA 50 levels, and the difference in sensitivity and specificity was marginal. In clinical practice the greatest value of CA 19-9 and CA 50 is in the diagnosis of pancreatic cancer.