Evaluation of thymidylate synthase and ERCC1 mRNA levels as predictive markers in colorectal cancer patients treated with S-1 and oxaliplatin

e15071 Background: Oxaliplatin has been widely used for the treatment of colorectal cancer. The mechanism of action of platinum compounds such as oxaliplatin is to bind to a DNA molecule in the form of a platinum-DNA-adduct. Excision repair cross complementation group 1 (ERCC1), which plays a major role in the nucleotide excision pathway, has a polymorphism in codon 118, and is reported to be associated with a resistance to platinum-based therapy. Thymidylate synthase (TS) and dehydropyrimidine dehydrogenase (DPD) are key enzymes of 5-FU metabolism and are well known to be associated with a response to 5-FU-based therapy. Methods: Twenty-one colorectal cancer patients (male:female = 7:14; median age, 65) treated with a combination of oxaliplatin and S-1 as a first-line therapy were analyzed for ERCC1 codon 118 polymorphism and the mRNA expression levels of TS, ERCC1, and DPD. Formalin-fixed paraffin- embedded surgical specimens were used and t-RNA and DNA were extracted. The mRNA expression levels were me...