Gene expression for dihydropyrimidine dehydrogenase and thymidine phosphorylase influences outcome in epithelial ovarian cancer

Purpose: Dihydropyrimidine dehydrogenase (DPD) is a pyrimidine salvage enzyme responsible for degradation of thymine, which is produced from thymidine by thymidine phosphorylase (TP). Our purpose was to determine whether DPD affects prognosis in patients with epithelial ovarian cancer and how the two enzymes may interact in such effects. Patients and Methods: DPD gene expression was analyzed by reverse transcription-polymerase chain reaction in 27 samples from normal ovaries and the 85 epithelial ovarian cancers previously studied with regard to TP gene expression. Results: DPD gene expression was significantly lower in epithelial ovarian cancers than in normal ovaries (P < .0001), whereas TP gene expression and the ratio of TP to DPD gene expression (TP:DPD) were significantly higher in epithelial ovarian cancer (P < .0001 for both). In patients with epithelial ovarian cancer, DPD gene expression and the TP:DPD ratio did not significantly correlate with any clinicopathologic factors. Patients with a high TP:DPD ratio (higher than the median) had significantly poorer outcomes than those with lower ratios (P = .0002). The difference in survival between groups with high and low TP:DPD ratios was greater than the difference between groups with high and low TP gene expression. Multivariate analysis showed the TP:DPD ratio to be the independent prognostic factor (P = .0002). In tumors with high TP gene expression, low DPD gene expression significantly correlated with poor survival (P = .04). Conclusion: Downregulation of DPD gene expression may enhance the negative prognostic effect of high TP gene expression in patients with epithelial ovarian cancer. Certain newly available chemotherapeutic choices may take the TP:DPD ratio into consideration.