Tumor M2-pyruvate kinase (M2-PK) is up-regulated in proliferating tissues. It has been shown that tumor M2-PK is detectable and quantifiable in the stool and plasma of patients with colorectal cancer (CRC). Tumor M2-PK has been extensively studied in gastrointestinal tumors but its role in other cancer types has not yet been deeply evaluated. The aim of the study was to determine and compare plasma tumor M2-PK levels in different cancer types. All patients undergoing diagnostics for cancer at our Hospital during 2011 were included in the study (n=139). Plasma tumor M2-PK concentration was analyzed by an enzyme-linked immunosorbent assay. The different cancer types found in the study were: 60 colorectal, 43 breast, 8 lung, 5 prostatic, 4 ovarian and the remaining 19 cases were other uncommon tumor types. Most tumors had high concentrations of tumor M2-PK; prostatic, pharyngeal and testicular tumors had levels lower than or near the cut-off. Plasma tumor M2-PK levels were significantly higher in patients with distant metastases and stage IV by TNM. Plasma tumor M2-PK is not a specific marker for CRC and is elevated in many other types of cancers, including breast, lung, ovarian, and thyroid. Small amounts are found in prostatic, pharyngeal and testicular tumors.