Creatine Kinase (CK)-MB-to-Total-CK Ratio: a Laboratory Indicator for Primary Cancer Screening

Background: For the determination of creatine kinase (CK)-MB, the immunoinhibition method is utilized most commonly. However, the estimated CK-MB activity may be influenced by the presence of CK isoenzymes in some conditions like cancer. Thus, a CK-MB-to-total-CK ratio more than 1.0 could be found in such a situation. The study aimed to explore the relationship of cancer to high CK-MB-to-total-CK ratio. Materials and Methods: From January 2011 to December 2014, laboratory data on all CK-MB and total CK test requests were extracted at Far Eastern Memorial Hospital (88,415 requests). Patients with a CK-MB-to-total-CK ratio more than 1.0 were registered in this study. Clinical data including tumor location, tumor TNM stage and metastatic status were also collected. Results: A total of 846 patients were identified with a CK-MB-to-total-CK ratio more than 1.0. Of these, 339 (40.1%) were diagnosed with malignancies. The mean CK-MB-to-total-CK ratio was significantly higher in malignancy than in non-malignancy ($1.35{\pm}0.28$ vs $1.25{\pm}0.23$, p<0.001) groups. The most frequent malignancy with a CK-MB-to-total-CK ratio more than 1.0 was colorectal cancer ($1.42{\pm}0.28$, 16.5%, n=56), followed by lung cancer ($1.38{\pm}0.24$, 15.9%, n=54) and hepatocellular carcinoma (14.5%, n=49). Higher CK-MB-to-total-CK ratios in hematological malignancies ($1.44{\pm}0.41$)were also noted. Additionally, the CK-MB-to-total-CK ratio was markedly higher in advanced stage malignancy than in early stage ($1.37{\pm}0.26$ vs. $1.29{\pm}0.31$, p=0.014) and significantly higher in liver metastasis than in non-liver metastasis ($1.48{\pm}0.30$ vs. $1.30{\pm}0.21$, p<0.001). Conclusions: The CK-MB-to-total-CK ratio is an easily available indicator and could be clinically utilized as a primary screening tool for cancer. Higher ratio of CK-MB-to-total-CK was specifically associated with certain malignancies, like colorectal cancer, lung cancer and hepatocellular carcinoma, as well as some cancer-associated status factors such as advanced stage and liver metastasis.