Thymidylate Synthase Gene Polymorphism and Survival of Colorectal Cancer Patients Receiving Adjuvant 5-Fluorouracil

Limited studies indicate a possible association of 5-UTR thymidylate synthase enhancer region polymorphism and treatment outcome in patients medicated with 5-fluorouracil (5-FU). The study was designed to verify the relationship in patients with colorectal cancer (CRC), a Polish population that received 5-FU-based adjuvant chemotherapy. The study analyzed 145 Astler-Coller B2 and C CRC patients. Genotyping for a variable number of tandem repeats and G to C single-nucleotide polymorphism in the 5-UTR of the thymidylate synthase (TS) gene was carried out. TS genotypes were classified into high expression (high TS) and low expression types (low TS). High TS was found in 22.8% of patients. The right-side tumors were more frequently associated with high TS than the left-side tumors (p=0.024). High TS was only found in 9.3% of rectal tumors, but in 29.7% of colon cancers (p=0.0042). Disease-free survival after 20 months (DFS 20) was longer in subjects with low TS than in high TS (p=0.043). Patients who underwent chemotherapy had longer DFS 20 in the low TS than in the high TS subgroup (p=0.051). The low TS was found to be an independent good prognostic factor for DFS 20 in the whole group as well as in the subgroup treated with chemotherapy (p=0.024 and p=0.034, respectively). Patients with low TS did not show any differences in DFS 20 whether they were treated with adjuvant chemotherapy or not. Proximal CRC tumors are characterized by higher TS expression genotypes than distal tumors, and are at significantly greater risk of early recurrence during the first 20 months after surgery.