Ectopic Production of Creatine Kinase MB: Updated Evaluation by Mass Assays

There have been several reports of apparently high concentrations of creatine kinase (CK)-MB in the sera of cancer patients (1)(2)(3)(4). In several of these cases, the high activity resulted from the presence of macro CK types 1 and 2 (5). False-positive results for CK-MB can occur if nonspecific assays such as immunoinhibition are used (6). These atypical isoenzymes are not inhibited by anti-CK-B antibodies, and high apparent CK-MB activities are produced. Macro CK type 1 (CK-BB bound to IgG) migrates between CK-MM and -MB, whereas type 2 (polymeric mitochondrial CK) migrates cathodic to CK-MM and can be readily differentiated from CK-MB by electrophoresis (7). However, macro CK-BB linked to IgA can comigrate with CK-MB, and false-positive detection of MB is possible even with electrophoresis (8).Annesley and McKenna (9) published the one clear case of ectopic CK-MB production by a tumor, by demonstrating high concentrations of CK-MB in homogenized tumor tissue and ruling out the presence of macro CK forms by heat stability tests. We describe a second case in which persistently high concentrations of CK-MB were detected in a patient with metastatic cancer. CK isoforms, myoglobin, lactate dehydrogenase isoenzymes, and cardiac troponins T and I were used to rule out the presence of acute myocardial injury.A 71-year-old white man with a past medical history of coronary artery disease, acute myocardial infarction (AMI), hypertension, congestive heart failure, cerebrovascular accident, carotid stenosis, and atrial fibrillation presented to the Hospital of St. Raphael with a 4-day history …