Influence of thymidylate synthase expression on survival in patients with colorectal cancer

Background: Thymidylate synthase (TS) plays a critical role in nucleotide metabolism and is an important target for 5-fluorouracil (5-FU), the standard chemotherapeutic drug for treatment of colorectal cancer (CRC). Aims and Methods: The present study aimed to evaluate TS variable number tandem repeat sequences (VNTR) polymorphism by polymerase chain reaction and TS protein expression by immunohistochemistry and its association with clinicopathological parameters in untreated CRC patients (n = 100). Further, the prognostic and predictive role of TS has been evaluated. Results: For TS VNTR polymorphism, the observed frequencies of 2R/2R, 2R/3R, and 3R/3R genotypes were 22%, 51%, and 27%, respectively. When immunohistochemical localization was studied, cytoplasmic staining for TS was observed in 70% of patients. A significant inverse correlation was noted between TS protein expression and tumor, node, metastasis staging (P = 0.027), Dukes' staging (P = 0.039), and lymph node status (P = 0.012) of CRC patients. However, there was no significant correlation between TS VNTR polymorphism and TS protein expression. On survival analysis, a significantly shorter overall survival (OS) was seen in CRC patients with negative protein expression (P = 0.031). Moreover, the subgroup of CRC patients treated only with surgery also showed a trend of poor OS in patients with negative TS protein expression (P = 0.058). However, neither TS polymorphism nor its protein expression was able to predict relapse-free survival. Conclusion: Negative TS protein expression may be related to unfavorable clinical outcome in CRC patients. However, further studies in a larger set of patients are necessary to better assess TS as a prognostic and predictive marker for 5-FU response in CRC patients.