Radioimmunoassay of serum creatine kinase-BB as a tumour marker in breast cancer.

Brain type creatine kinase-BB (CPK-BB) was measured by radioimmunoassay in the serum of 113 women with breast cancer and 354 female controls. 80% of women with metastatic breast cancer had levels above 3 ng/ml (control range 0.5--3.7 ng/ml); the highest level was 23 ng/ml. 60% of women with local disease but no evidence of distant metastases showed levels above 3 ng/ml, the highest being 9.0 ng/ml. Of women who had presented with stage I, II, or III disease and postoperatively had no evidence of persistent disease 30% had levels above 3 ng/ml. Serial measurements in 31 patients indicated that the serum CPK-BB correlated with clinical response to treatment.