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Tumor type M2-pyruvate-kinase levels in pleural fluid versus plasma in cancer patients: a further tool to define the need for invasive procedures

^a Department of Thoracic Surgery, Tor Vergata University, Viale Oxford 81, I-00133 Rome, Italy
^b Department of Internal Medicine, Tor Vergata University, Viale Oxford 81, I-00133 Rome, Italy
^c Thoracic Surgery Unit, AORN Cardarelli, Via A., Cardarelli 9, 1-80130 Naples, Italy

Received 13 July 2007; received in revised form 19 December 2007; accepted 16 January 2008.

^_* Corresponding author. Tel.: +39 0620902882; fax: +39 0620902894. (Email: elia{at}med.uniroma2.it).

Objective: Pleural effusion is a common diagnostic problem and a challenge to the thoracic surgeon. The analysis of serum and body fluids for tumor markers is an established diagnostic procedure. Among various markers, tumors are linked to the overexpression of a glycolytic isoenzyme, M2-pyruvate-kinase (M2-PK). This preliminary study evaluated this enzyme as a tumor marker to differentiate malignant from benign pleural effusion. Methods: The tumor M2-PK concentration was measured in the EDTA-plasma and pleural fluid of 34 patients with an established diagnosis of cancer, either primary of the chest (18) or secondary to chest (16) and in 34 controls with benign effusion. The concentration was quantitatively determined by an enzyme-linked immunosorbent assay. The cut-off level between negative and positive values of the tumor M2-PK was defined as the benign group's mean + 2SD (95% percentile). True-positives, false-positives, true-negatives, and false-negatives, were determined with ‘positive’ referring to histologically proven malignant effusion and ‘negative’ referred to as nonmalignant effusions. Sensitivity, specificity, positive predictive value, and negative predictive value were assessed. Results: The cut-off value was established at 7.61 U/ml for plasma and 32.9 U/ml for pleural fluid. Both plasma and pleural fluid levels of tumor M2-PK were significantly higher in patients with known chest malignancy, either primary or metastatic, compared to nonmalignant effusions (p < 0.001). Sensitivity in pleural fluid was significantly higher compared to plasma (85.7% vs 76.2%; p < 0.01). Moreover, negative predictive value was higher for pleural fluid compared to plasma (79.4% vs 70.8; p < 0.01) Conclusions: Tumor M2-PK marker is useful in differentiating malignant from benign pleural effusions. Moreover, its sensitivity and NPV in pleural fluid are significantly higher compared to plasma. The usefulness of such a test is not strictly diagnostic but aims at excluding poorly performing patients from further invasive procedures. Thus, the inclusion of M2-PK within a panel of well-known tumor markers such as CEA, MCA, Ca 125 and Ca 19-9, may help in increasing the overall sensitivity and specificity.

Key Words: Pleural effusion • Tumor markers • M2-pyruvate-kinase • Thoracoscopy • Enzyme immunoassay • Thoracic malignancies • Diagnostic procedure