Serum levels of a human lung tumor-associated antigen using an improved radioimmunoassay.

A human lung tumor-associated antigen, previously purified to apparent homogeneity from an extract of a small cell tumor, was radioiodinated with Bolton-Hunter reagent for use in a competitive protein-binding radioimmunoassay. A panel of 215 sera was assembled from normal individuals and pretreatment patients with lung cancer, benign lung disease, and nonlung cancers, and lung tumor antigen in each was quantitated using the radioimmunoassay. The mean of normals was 0.92 +/- 0.43 (S.D.) microgram/ml (n = 88), and values greater than 2 standard deviations above the mean (1.78 micrograms/ml) were considered positive. Positive rates in lung cancers of the following histological types were found: adenocarcinoma, 60% (9 of 15); squamous cell, 42% (13 of 31); large cell, 17% (3 of 18); and small cell, 19% (3 of 16). In addition, 13% (3 of 23) of other cancers, 0% (0 of 24) of benign lung disease, and 2% (2 of 88) of normals were positive. Approximately one-third of Stage 1 patients in the squamous cell and adenocarcinoma groups were positive while two-thirds of patients with more advanced Stage III disease in these categories showed elevations.