Relationship between thymidylate synthase (TYMS) gene polymorphism and TYMS protein levels in patients with high-risk breast cancer.

The thymidylate synthase gene (TYMS) has three functional polymorphisms which are associated with TYMS expression. To explore the predictability of TYMS polymorphisms for the sensitivity and toxicity of 5-fluorouracil (5-FU) in breast cancer patients, this study investigated the association between TYMS polymorphisms and TYMS protein expression in normal and tumour tissue specimens from 49 lymph node-positive breast cancer patients. An analysis of the TYMS 3'-UTR polymorphism showed that level of TYMS protein in normal tissue with the +6 bp/+6 bp genotype was significantly higher than that for the -6 bp/+6 bp genotype. Tumour tissue with the +6 bp/+6 bp genotype had a significantly higher TYMS protein expression than did those with other genotypes. These findings suggest that breast cancer patients with the TYMS 3'-UTR +6 bp/+6 bp polymorphism whose tumours show a 6 bp deletion within TYMS 3'-UTR represent a group that may derive the most benefit from 5-FU chemotherapy.