Plasma levels of tumor M2-pyruvate kinase should not be used as a tumor marker for hematological malignancies and solid tumors.

It has been reported that the dimeric isoform of the enzyme pyruvate kinase M2 was overexpressed in various solid tumor cells. Hence, it was suggested that circulating levels of the so-called tumor M2-pyruvate kinase (Tu M2-PK) could be used as a tumor marker for monitoring systemic therapies of various solid tumors. We analyzed its validity as a tumor marker by comparing plasma levels of Tu M2-PK in patients with different non-malignant diseases to levels in healthy individuals and in patients with hematological diseases. Plasma levels of Tu M2-PK were measured using an ELISA assay in a total of 284 patients. The mean Tu M2-PK concentration of 32 U/mL was significantly higher in the group of patients with hematological malignancies (n = 121) (p < 0.001). However, 37% of healthy individuals (n = 63) and 44% of patients with non-malignant diseases (n = 100), especially patients with an acute inflammatory reaction (67%), were found to have elevated levels of Tu M2-PK using a cutoff level of 15 U/mL. The specificity was 59% and the sensitivity was 51%. There was no significant correlation between the prevalence of a hematological malignancy and positive Tu M2-PK result. Thus, our data imply that Tu M2-PK is not a useful tumor marker for hematological malignancies and solid tumors, as a significant number of false positive results were detected in healthy individuals and patients with non-malignant diseases.