Prognostic and predictive value of the thymidylate synthase expression in patients with non-metastatic colorectal cancer.

AIMS: To assess the value of thymidylate synthase (TS) expression as a predictive factor in the efficacy of adjuvant chemotherapy in colorectal cancer, as well as its independent prognostic value for survival.
METHODS: We studied 114 high risk colorectal carcinoma patients (high risk stage II and stage III), distributed in two treatment groups: surgery alone (61 patients) or surgery followed by 5-FU-based chemotherapy (53 patients). TS protein expression in the tumour tissue was assessed by immunohistochemistry.
RESULTS: In the surgery alone subgroup, overall survival (OS) at 5 years were 77.5% for the patients with low TS expression, against 57.7% for the patients with high TS expression (p=0.006). Among patients with low TS, there was no difference in OS as a result of whether adjuvant chemotherapy was carried out or not (65.8 vs 77.5%, p=0.29). Among the patients with high TS, there was a significant gain in OS in favor of chemotherapy (87.8 vs 57.7%, p=0.04). Analyzing the complete sample, TS expression was not shown as an independent prognostic factor for survival in the multivariate analysis.
CONCLUSIONS: The immunohistochemical TS expression may be used for selecting patients for better adjuvant chemotherapy protocols. In this sample, TS expression was not an independent prognostic factor for survival.