Detection of the neural cell adhesion molecule (NCAM) in serum of patients with small-cell lung cancer (SCLC) with 'limited' or 'extensive' disease, and bone-marrow infiltration

The neural cell adhesion molecule (NCAM) is a tumour-related antigen found on the surface of small-cell lung cancer (SCLC). NCAM exists in several molecular forms, including a soluble isoform. We have measured serum levels of NCAM using an enzyme immunoassay with 2 antibodies, NCC-LU-246 and NCC-LU-243, that react with different epitopes on the NCAM molecule. NCAM activity from 83 patients with active SCLC, either pre-treatment, progressing or in relapse was significantly higher than in 70 patients on follow-up. Overall, 40% of patients with active SCLC and 7% patients on follow-up had serum levels of NCAM > 2SD above controls; 61% of patients with relapsed SCLC had elevated levels of NCAM. Pre-treatment NCAM levels were significantly higher in 35 patients with "extensive" disease than in 19 patients with "limited" disease. Serum NCAM activity was also significantly higher in patients with tumour infiltration of the bone marrow. This difference could not be explained solely by the presence of "extensive" disease. Serum NSE levels in these patients were correlated with NCAM activity. The presence of raised serum NCAM in active disease and in patients in relapse suggests that this antigen could be used as a target for antibody-directed therapy of micrometastases.