Sialosylated Lewisx in the sera of cancer patients detected by a cell-binding inhibition assay.

A new cell-binding inhibition assay to detect tumor-associated antigens in sera was developed. This assay determined that sialosylated Lewisx, as detected by the CSLEX1 monoclonal antibody, is present in the sera of 95% of patients with advanced lung adenocarcinomas. Sera with inhibition titers of 1:16 or higher were presumed to contain sialosylated Lewisx. Tests of over 900 sera samples from both malignant and benign disease patients yielded the following percentages of positive inhibition: lung cancers, 43.8%; stomach cancer, 26.0%; colon cancer, 44.4%; gall bladder and bile duct cancers, 47.8%; pancreas cancer, 37.5%; breast cancer, 26.7%; cancers of the hematopoietic system, 2.9%; benign diseases, 0.9% (332 sera); and normal healthy donors, 0.7% (280 sera). Within the lung cancer group, 95% of the sera from 21 advanced (Stages III and IV) nontreated adenocarcinoma patients gave positive results with high inhibition titers, whereas only 27% of sera from treated advanced adenocarcinoma patients yielded positive results. The sensitivity of the cell-binding inhibition assay is similar to those of the solid-phase radioimmunosandwich and reverse passive-hemagglutination assays. Reproducibility tests yielded an r value of 0.90. These results suggest that this simple cell-binding inhibition assay could be applied with monoclonal antibodies, such as CSLEX1, to monitor cancer.