Measurement of serum thymidine phosphorylase levels by highly sensitive enzyme-linked immunosorbent assay in gastric cancer.

Thymidine phosphorylase (TP) is an enzyme that converts 5'-DFUR to 5-FU and also acts as an angiogenic factor. Measurement of serum TP levels has recently become possible by highly sensitive enzyme-linked immunosorbent assay (ELISA). We examined 38 patients with gastric adenocarcinoma to measure serum TP levels by highly sensitive ELISA method and tissue TP levels by conventional ELISA. In addition, immunohistochemical staining of normal and cancer tissues was also performed. Serum TP levels in patients with stages III and IV and inoperable or recurrent cancer were significantly higher than those in healthy controls. A high correlation was found between serum TP levels and tumor TP levels (r=0.65, p<0.0001). Moreover, serum TP levels were about 1/2500 of tumor TP levels. Tissue TP values in tumor were significantly higher than those in normal tissue. On the other hand, no significant differences among the cancer stages were found in either serum or tumor tissue. In conclusion, we demonstrate that serum TP levels strongly reflect tumor TP levels, and it may predict clinicopathological factors, prognosis, or sensitivity of anti-cancer drugs.