Objective To evaluate the diagnostic value of Tumor M2 PK in patients with breast cancer.Methods Tumor M2 PK was quantitatively detectable in EDTA plasma with a sensitive enzyme linked immunosorbent essay.So far,70 newly diagnosed breast cancer patients and 50 benign breast diseases patients were included.Results The concentration of Tumor M2 PK in breast cancer patients were significantly higher than benign breast diseases group(P0.01).The concentration of Tumor M2 PK correlated strongly with the tumor stage,showing significantly increasing concentration with progressive tumor.The concentration of Tumor M2 PK was higher in patients with lymph node metastasis than those without metastasis(P0.01).The receiver operation characteristic analysis showed the cut off value of Tumor M2 PK was set at 13.3 U/mL.The sensitivity,specificity,positive predictive value,negative predictive value and accuracy of Tumor M2 PK in detecting breast cancer was 67.1%,80.0%,82.5%,63.5% and 72.5%,respectively.Conclusions Tumor M2 PK may be a tumor marker available for the detection of breast cancer and it is valuable for the prediction of clinical stage and metastasis of breast cancer.