Diagnostic value of tumor M2-pyruvate kinase in neuroendocrine tumors. A comparative study with chromogranin A

Objective: M2-pyruvate kinase isoenzyme (M2-PK) is expressed by undifferentiated or proliferating tissue. The aim of the study was to establish the diagnostic role of tumor M2-PK (TM2-PK) in patients with neuroendocrine tumors and to compare its diagnostic value with that of chromogranin A (CgA) which is well-established. Materials and Methods: Forty-nine patients with proven neuroendocrine tumors were divided as follows: subgroup A (17 patients in whom the tumor was surgically removed), subgroup B (9 patients with the neoplasm without metastases) and subgroup C (23 patients with tumor and distant metastases). Twenty-four healthy subjects were also studied as controls. Plasma TM2-PK and CgA were measured using ELISA techniques. Results: TM2-PK concentrations (cut-off value 5.6 U/mL) were abnormally high in 25.0% of the healthy subjects, in 41.2% of the patients of subgroup A, in 66.7% of those of subgroup B and in 78.3% of those of subgroup C. CgA concentrations (cut-off value 5.0 U/L) were normal in all healthy subjects, whereas they were abnormally high in 76.5% of the patients of subgroup A, in 88.9% of those of subgroup B and in 95.7% of those of subgroup C. Conclusion: Since TM2-PK has a sensitivity similar to that of CgA while its specificity is significantly lower (p=0.031), it seems. of limited value in detecting neuroendocrine tumors.