Elevated serum CK-MB and CK-BB isoenzymes in a patient with small cell lung cancer: a case report.
An increase in serum creatine kinase-MB (CK-MB) isoenzyme is regarded as a specific indication of acute myocardial infarction. Recently, increased concentrations of various types of creatine kinase isoenzymes (mostly CK-BB and macro CK type 2 isoenzymes) have been found in the blood of some patients with malignancies. However, highly elevated serum CK-MB isoenzyme associated with malignancy has rarely been reported previously. Herein a case of extensive small cell lung cancer is presented in which the elevated serum levels of CK were detected throughout the three weeks of hospitalization. Fractionation of its isoenzymes by gel electrophoresis displayed elevated CK-MB and CK-BB isoenzymes. The proportion of serum CK-MB and CK-BB isoenzyme activities was persistently above normal (CK-MB 50-53%, normal < 5%). Clinical examination showed no evidence of myocardial infarction or injury, or tumor involvement of the heart. The tumor was the probable source of most circulating CK-MB isoenzyme. In clinical practice, markedly elevated levels of CK-MB, or increased levels of CK-MB in combination with CK-BB may point away from a myocardial origin and toward the existence of a malignancy.