An improved antigenic marker of human lung carcinomas and its use in radioimmunoassays.

An antigenic activity in pleural effusions of patients with squamous-cell carcinoma of the lung has been prepared in highly purified form by a 5-step fractionation scheme. The purified substance, designated LuCA (lung cancer antigen), was assessed during the course of the fractionation procedure by a radioimmunometric assay carried out with specific soluble reagents. Sensitive saturation-binding assays showed no or only weak uptake of the 125I-labelled antigen preparation by a panel of antisera specific for known bronchogenic tumour markers, and for normal human serum proteins. The preparation appeared to contain lung-tumour-associated antigens, one of them probably distinct for squamous-cell carcinomas. The antigen fraction consists of acid-soluble glycoproteins, and was demonstrated by SDS-polyacrylamide gel electrophoresis as a single band in the mol. wt region of 43,000. The gel-filtration elution volume appeared to indicate the occurrence of the antigenic activity in multiples of this smaller unit. Pilot radioimmunoassays performed with LuCA and an absorbed specific antiserum suggest the possible suitability of the marker preparation for screening lung-cancer patients.