High creatine kinase MB isoenzyme activity associated with a rhabdomyosarcoma.

A 20-year-old man was found to have high plasma creatine kinase (EC 2.7.3.2) activity in association with a rhabdomyosarcoma of the prostate. There was a very high proportion of the MB isoenzyme. Clinical findings and changes in creatine kinase activity with time showed that this increase was not ascribable to myocardial disease. We believe that the high proportion of CK-MB, confirmed by a combination of electrophoretic and immunoinhibition studies, originated from the tumor.