Aim: Evaluation of thymidine phosphorylase (TP), dihydropyrimidine dehydrogenase (DPD), and thymidylate synthase (TS) mRNA levels in formalin-fixed, and paraffin-embedded tissues of patients with colorectal cancer and their prognostic and/or predictive value.
Materials and methods: Total RNA was isolated from microdissected, formalin-fixed, and paraffin-embedded tissues (controls and tumor) and subjected to quantitative RT-PCR (QRT-PCR) in the LightCycler system. Resulting mRNA levels correlated to tumor histology (n=102) and the clinical follow-up in patients treated by resection alone (n=40) and by resection plus adjuvant 5-FU-based chemotherapy (n=52).
Results: Correlation to histopathological parameters revealed a significant association between tumor stage and the TP mRNA level (T and N category and UICC) as well as the TP:DPD (T and N category and UICC) and TS:DPD (T category) ratio. In addition, tumor differentiation was correlated to the TS mRNA level and the TS:DPD ratio. Finally, the TS:DPD ratio was a prognostic marker for overall survival in patients receiving resection alone (p=0.032). Moreover, a high TP:DPD ratio (>8.1; p=0.002) and, marginally, low DPD (<8.2; p=0.05) mRNA levels significantly correlated to disease-free survival.
Conclusion: We present a novel, standardized approach for TP, DPD, and TS mRNA quantification in archival tissue specimens and applied this to a large series of primary colorectal tumors. Correlations to histopathological parameters and clinical follow-up revealed an association of TP, DPD and TS mRNA expression patterns with tumor stage and suggested new prognostic and predictive markers for patients with colorectal cancer.