Differences in expression of SPan-1 and CA15-3 antigens in blood and tissues

Pancreatic and mammary cancer cells are reported to have different oligosaccharides on the same apomucin, the MUCI gene product. A better understanding of the tissue specificity of these sugar structures may help in identifying the source of mucins when they are found in the sera. Serum levels of 3 pancreatic-cancer-associated carbohydrate epitopes identified by monoclonal antibodies (MAbs) SPan-1, 19-9 and DU-PAN-2, were compared to those of CA15-3 in a variety of malignant conditions. CA15-3 identifies both carbohydrate and peptide determinants associated with the MUC1 apomucin in breast tissues. SPan-1 antigen was elevated in a high percentage of patients with pancreatic, gastric and colorectal cancer but in only a few of the patients with malignancies of non-GI origin such as breast, ovary and lung. The 19-9 and DU-PAN-2 antigens had a similar pattern of much greater sensitivity for pancreatic cancer than for these non-gastrointestinal cancers. The levels of these 3 markers showed significant correlations in pancreatic cancer. In contrast, CA15-3 was elevated in a large number of patients with breast, lung, ovarian and pancreatic cancers. There was no correlation of CA15-3 with the 3 other markers in pancreatic cancer. SPan-1 and DF3/115D8 antigens in blood have different mobilities in SDS-PAGE and buoyant densities. Moreover, SPan-1 and DF3 antigenic determinants are localized in different regions of the same normal and malignant pancreas and breast tissues. Thus the SPan-1 determinant can be dissociated from the breast peptide and/or carbohydrate determinants.