Isoenzyme pattern of enolase in the diagnosis of neuroendocrine bronchopulmonary tumors.

Electrophoretic separation of enolase isoenzymes and the measurement of enolase activity were performed in 25 lung tumor extracts. In 13 neuroendocrine (NE) tumors (nine small cell lung carcinoma [SCLC], three atypical NE tumors, and one carcinoid tumor), the NE differentiation was assessed by ultrastructural determination of neurosecretory granule (NSG) density. Twelve non-NE lung tumors also were studied (three adenocarcinomas, four epidermoid, two composite, two large cell undifferentiated carcinomas, and one lymphoma). Four normal lung tissues and 1 human brain were used as controls. The gamma gamma isoenzyme was present at a high level (mean +/- SE, 12 +/- 3%) in all NE carcinomas and consistently absent in all non-NE tumors as well as in normal lung. The alpha gamma isoenzyme was found in significantly higher proportion in NE carcinomas (mean +/- SE, 29 +/- 2%) than in non-NE tumors (mean +/- SE, 8 +/- 1%) (P less than 0.0001), despite an equally high level of total enolase activity in both groups of tumor. The separation of alpha gamma and gamma gamma isoenzymes of enolase allows for the accurate diagnosis of NE tumors and NE components of atypical NE carcinomas, and the gamma gamma isoenzyme, in contrast to gamma chain detection by immunoassay, can be considered to be a specific marker in itself of NE differentiation in lung neoplasms.