Quantitative distribution of cluster 1 small cell lung cancer antigen in cancerous and non-cancerous tissues, cultured cells and sera.

Three monoclonal antibodies (mAbs), NCC-LU-243, -244 and -246, detected three different epitopes on a 145-kDa cell membrane antigen, which had been designated as the cluster 1 antigen at the First International Workshop on Small Cell Lung Cancer (SCLC) Antigens. The distribution of the antigen in various tissues, cultured cells and sera was examined by immunohistochemistry and sandwich radioimmunoassay using these mAbs. The antigen is a normal differentiation antigen and is present in neuronal, neuroendocrine and cardiac muscle cells. The level of the antigen was highest in central nervous tissues, while it was undetectable in the liver, kidney and peripheral lung. Among tumor tissues, the antigen was detected only in SCLC, carcinoid tumor and neuroblastoma, indicating its usefulness as a marker for discriminating SCLC from non-SCLC. The level of the antigen varied among SCLC tissues and tended to be lower in variant-type cultured SCLC cells. Although an increase in the antigen level was observed in sera of some patients with advanced SCLC, the antigen did not possess any additional value over neuron-specific enolase as a serum tumor marker for monitoring SCLC patients.