Abstract
An unusual clinical laboratory phenomenon-serum creatine kinase-MB (CK-MB) activity exceeding total creatine kinase (CK) activity (CK-MB > CK)-is frequently observed in cancer patients, yet its molecular origin and relevance to tumor biology remain unclear. We conducted an integrated analysis combining a large retrospective cancer cohort (n = 1,651), serum CK isoenzyme electrophoresis, and qRT-PCR analysis of paired serum and platelet samples. Public RNA-sequencing datasets, including tumor-educated platelets (TEPs) and single-cell data from lung cancer metastases, were utilized to explore the molecular basis and clinical significance of CK isoenzyme alterations. Colorectal and lung cancers were the most frequently associated malignancies with CK-MB > CK abnormalities, particularly in advanced stages. Electrophoresis and transcript profiling revealed that this paradoxical elevation was driven by aberrant increases in non-cardiac CK isoenzymes, especially brain-type creatine kinase (CK-BB) and mitochondrial CK. A composite index (CK-Sub), integrating CK-BB and mitochondrial CK isoforms, was developed and found to be potentially associated with tumor progression. Notably, CKB mRNA was significantly elevated in platelets from lung cancer patients and exceeded paired serum levels, with a strong positive correlation (R2 = 0.33, p < 0.001), suggesting that platelets may contribute to the circulating isoenzyme pool. This observation was supported by the TEPs RNA-seq data, which confirmed higher CKB expression in lung cancer patients (p = 7.7 × 10⁻11). Single-cell RNA-seq analysis further showed that CKB expression was enriched in metastatic tumor cells but not in primary lesions. Functional gene enrichment analysis revealed associated pathways involved in metabolism, oxidative stress, and intercellular signaling. Our findings suggest that platelet-related CKB may be linked to metastatic potential in lung cancer and represent a previously underrecognized component in cancer-associated biochemical alterations. This study provides novel insights into the non-canonical roles of platelets in cancer biology and highlights CK isoenzyme profiling as a clinically relevant tool for tumor characterization.