Levels of creatine kinase and its BB isoenzyme in lung cancer specimens and cultures.

Small-cell carcinomas of the lung (SCCL) have properties of amine-handling cells, and high levels of the key amine-handling cell enzyme L-dopa decarboxylase (EC 4.1.1.28) distinguish SCCL from most other lung cancers. SCCL tumor specimens and continuous cultures also are characterized by high levels of creatine kinase (EC 2.7.3.2) and its BB isoenzyme (CK-BB). Electrophoretic analysis of creatine kinase isoenzymes indicated that creatine kinase levels in SCCL were quantitatively but not qualitatively different from those in normal lung and other lung cancers. Supernatant fluids of SCCL cultures contained relatively modest concentrations of CK-BB but lacked detectable L-dopa decarboxylase activity. Variant SCCL cultures with altered morphology lost their amine-handling properties, including L-dopa decarboxylase activity, but retained high levels of CK-BB, indicating discordant expression of the two enzymes. CK-BB levels were measured in the sera of 67 patients having SCCL. Elevated levels were present in 16 of 41 patients (39%) having extensive-stage disease but in none of 26 patients (0%) having limited-stage disease.