Observation of a variant creatine kinase isoenzyme in sera and breast tumor cytosols.

A variant creatine kinase (CK) isoenzyme was identified in the sera of some patients who had advanced adenocarcinoma of the breast, stomach, and large intestine. A similar variant isoenzyme, together with a high concentration of CK-BB isoenzyme, was identified in some breast tumor cytosols. The variant creatine kinase activity in both sera and tumor cytosols was unaffected by antibodies specific for both the CK-M and DK-B subunits. This indicates that DK-MB isoenzyme determinations are currently best performed by electrophoretic rather than immunologic technics.