Orotate phosphoribosyl transferase (OPRT) is an essential nucleotide metabolic enzyme for cell proliferation and also a key enzyme for conversion of 5-FU to its active form in tumor tissue. The association between tumor OPRT activity and pathophysiological status, including lymph node metastasis [pN(+)], and the impact of OPRT for predicting pN(+) were investigated in gastric cancer. The lymph node status of 73 resectable gastric cancer patients was analyzed preoperatively by computed tomography (CT), ultrasonography and magnetic resonance, and the OPRT activity of collected tumor tissue was measured. Then these data were compared with pathological observation of a surgical lymph node specimen. OPRT activity in the tumor tissue decreased as the depth of invasion increased. An OPRT test demonstrated superior sensitivity and comparable accuracy and sensitivity for predicting pN(+), against current imaging diagnoses. Furthermore, the analysis of node negative patients by CT revealed that 80% of false negative patients were retrieved by this OPRT test. Thus, OPRT activity in tumor tissue was a powerful predictor of pN(+) in resectable gastric cancer, and the preoperative OPRT test, when it becomes possible, would provide a basis for accurate evaluation of disease status, which is indispensable for the planning of personalized therapy.

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