RESUMO
BACKGROUND/AIMS: Pyruvate kinase (PK) is a key enzyme of glycolysis. Different isoforms of this enzyme are tissue-specifically expressed (M2-PK, M1-PK, R-PK, L-PK). The concentration of the dimeric M2-PK is increased in a metabolic state of tumor cells. In this case, the dimeric M2-PK is termed Tumor M2-PK. We investigated EDTA-plasma of 73 patients with gastrointestinal (GI) cancer and 61 healthy controls to evaluate its significance in diagnosing GI cancer. METHODS: Plasma Tumor M2-PK was measured using an ELISA assay based on two monoclonal antibodies which specifically react with the dimeric Tumor M2-PK. RESULTS: The sensitivity of Tumor M2-PK was 67.1% for all GI cancers, that of CA 19-9 was 38.4% and that of CEA was 34.3%. The specificity of Tumor M2-PK was 91.8% (cutoff=20 U/mL). Tumor M2-PK showed a high sensitivity in gastric cancer (62.2%), colorectal cancer (66.7%) and bile duct cancer (75.0%). In colorectal cancer, the combination of Tumor M2-PK with CEA resulted in a remarkable increase in the sensitivity (86.2%). The average Tumor M2-PK levels were generally elevated in the metastatic GI cancer patients compared to nonmetastatic patients, especially in stomach cancer with statistical significance (p=0.005). CONCLUSIONS: Tumor M2-PK in EDTA-plasma seems to be a new valuable tumor marker in GI cancer.