Free CEA binding substance in cancer sera

In the serum of some cancer bearing patients we found a substance that bind carcinoembryonic antigen (CEA) and that was detectable by rabbit anti-goat antiserum for a cross-reaction phenomenon. We called this substance "CEA Binding Substance" (CBS). CBS was present only in patients with CEA negative tests. This substance found by radioimmunoassay, has been confirmed in an immunocytochemical study using sections of adenocarcinoma and normal tissue. CBS positive sera used as a first antiserum, showed a binding only with tumoral tissue using ABC peroxidase method; these sera developed an intense staining on tumor cells with a high tumor specificity.