Polymorphisms of thymidylate synthase as prognostic factor in rectal cancer.

Abstract

433 Background: Neoadjuvant fluoropyrimidine-based chemotherapy (ChT) plus radiotherapy (Rt) is a standard approach for locally advanced rectal cancer. Polymorphisms of thymidylate synthase (TS), the target for fluoropyrimidines, are recognized prognostic factors in colon cancer. The aim of this study was to evaluate the prognostic value of the polymorphisms of TS in rectal cancer after neoadjuvant ChT plus Rt. Methods: We studied one-hundred consecutive patients with stage II/III rectal cancer between November 2001 and March 2009. Patients underwent surgery 6-8 weeks after neoadjuvant Rt (5,040 cGy) plus fluoropyrimidine-based ChT. DNA was extracted from paraffin embedded biopsies. TS1494del6 and 5′-28bp repeat +G/C SNP polymorphisms were determined. Results: Sixty-seven percent were men and median age was 67 years. ypT stage was: T0 9%, T1 2%, T2 27%, T3 60% and T4 2%; 32% had locoregional adenopathies. The median follow-up was 45 months and relapse occurred in 20% of patients. Polimorphisms could be determined in 98% of pt: -6bp/-6bp 10%, - 6bp/+6bp 39%, +6bp/+6bp 51% and 2R/2R 72%, 2R/3R 21%, 3R/3R 6%. The grade of pathological tumour regression was not associated with polymorphisms. Relapses occurred in 40% of patients -6bp/-6bp, 22% of patients -6bp/+6bp and 21% of patients +6bp/+6bp. The difference in disease- free survival (DFS) between the first and the third groups was stadistically significative (p=0.049). No relation between 5′-28bp repeat +G/C SNP polymorphism and DFS was found. Conclusions: Our data suggest that the TS1494del6 polimorphism may be an important prognosis factor in rectal cancer receiving neoadjuvant chemoradiotherapy. No significant financial relationships to disclose.