Background: Mismatch repair genes fix problems that arise during deoxyribonucleic acid (DNA) replication when bases are incorrectly paired, as well as preventing microsatellite instability. Mutations are associated with an increased malignancy risk, including colorectal carcinoma. There are conflicting

reports concerning colorectal carcinoma with and without mismatch repair gene mutations in association

with disease outcome.

Objective: To correlate mismatch repair gene defects with the outcomes of colorectal carcinoma patients

having undergone adjuvant chemotherapy containing 5-fluorouracil.

Materials and methods: The records of all stage II, III and IV colorectal carcinoma cases treated at Songklanagarind Hospital from 1994-2003 were examined for the study. There were 140 patients and all had received adjuvant 5-fluorouracil-based chemotherapy. The mismatch repair gene proteins mutL homolog 1, colon cancer, nonpolyposis type 2 (E. coli) (MLH1) and mutS homolog 2, colon cancer, nonpolyposis type 1 (E. coli) (MSH2) in tumor cells were evaluated by immunohistochemistry. Negative staining confirmed abnormalities in or complete loss of mismatch repair genes. Survival analysis was carried out using the Kaplan-Meier method and the Cox Proportional Hazards regression.

Results: Mismatch repair gene defects were detected in 36 cases (25.7%): only MLH1 defects in 15 cases (10.7%), only MSH2 defects in 10 cases (7.1%), and both MLH1 and MSH2 defects in 11 cases (7.8%). Survival analysis showed no significant differences between mutated mismatch repair gene patients and normal mismatch repair gene patients (95% CI=0.35 to 0.67, p=0.54).

Conclusion: Mismatch repair gene defects do not predict the prognosis of colorectal cancer patients

treated with 5-fluorouracil-based chemotherapy.