Predictive value of thymidylate synthase expression in resected metastases of colorectal cancer.

Recent investigations have focused on the prognostic value of thymidylate synthase (TS) assessment in metastases of colorectal carcinoma (CRC). In order to evaluate the prognostic impact of TS expression after resection of metastases of colorectal cancer followed by systemic adjuvant chemotherapy, we performed an immunohistochemical characterisation of TS in the primary tumours and in the corresponding radically resected hepatic and pulmonary metastases. An additional objective was to compare the levels of TS in primary and metastatic disease. TS expression was assessed by immunohistochemistry using the monoclonal antibody TS 106. The study population consisted of 60 patients: 48 underwent liver and 12 lung resection. All of them received adjuvant chemotherapy after metastasectomy according to the Mayo Clinic schedule. In the 49 evaluable primary tumours, TS score was high in 53% and low in 47% of patients, while in the 60 metastatic samples TS immunostaining was high in 33% and low in 67%. There was a significantly smaller number of high TS expressors in metastatic than in primary tumours (P<0.04). No correlation was observed between TS expression and the site of the metastasis. TS status did not significantly correlate with the median disease-free interval (DFI) after metastasectomy, although this parameter was longer for patients with low TS immunoreactivity in the resected metastases than for those with high TS lesions (19.6 versus 13.8 months). Patients with high TS levels, however, had a significantly shorter median overall survival (OS) (27.6 months) than those with low TS expression (36.3 months) (P<0.008). TS status in the resected metastases confirmed its independent prognostic value in the multivariate analysis and was the only prognostic marker of OS in the subgroup of patients with resected liver metastases. These results suggest that high TS levels in resected metastases of colorectal cancer are associated with a poor outcome after surgery and 5-FU adjuvant therapy; therefore, a prospective assessment of TS levels in resected colorectal metastases could be useful to define which patients will most likely benefit from 5-FU adjuvant therapy after metastasectomy. Chemotherapeutic agents that target TS may not be the appropriate adjuvant treatment after metastasectomy for patients with a high TS expression in the resected metastases of colorectal cancer.