A New Serum Tumor Marker, CAM 123‐6, Highly Specific to Pulmonary Adenocarcinoma

KL‐6, a circulating mucin‐like glycoprotein, is a pulmonary adenocarcinoma‐associated antigen and is also regarded as an indicator of disease activity of interstitial pneumonitis. KL‐6 has extensive heterogeneous antigenic determinants and consists of multiple heterogeneous antigen molecules. We have searched for circulating KL‐6‐associated glycoproteins with superior diagnostic value to KL‐6 as a tumor marker for pulmonary adenocarcinoma. A new murine monoclonal antibody EH‐123 reacting with an asialosugar chain on KL‐6 was established. A new KL‐6‐associated molecule detected by a bimonoclonal bideterminant sandwich assay using the EH‐123 antibody as a catcher and horseradish peroxidase‐labeled KL‐6 as a tracer was designated as CAM 123‐6. In 59% (22 of 37) of patients with pulmonary adenocarcinoma, serum levels of CAM 123‐6 were abnormally elevated and the positive rate increased with the progression of clinical stage. Elevated levels were not detected in normal individuals or in patients with benign lung diseases, other histologic types of lung cancer, gastric cancer, colon cancer or breast cancer. CAM 123‐6 was more specific to pulmonary adenocarcinoma than carcinoembryonic antigen (CEA), but the sensitivity of CAM 123‐6 for pulmonary adenocarcinoma was similar to that of CEA. CAM 123‐6 is a promising candidate as a serum tumor marker for pulmonary adenocarcinoma.