We read with interest the study by Jover and colleagues (Gut 2006;55:848–55) on the predictive value of the DNA mismatch repair (MMR) or microsatellite instability (MSI) phenotype for response of colorectal cancer patients to 5-fluorouracil (5-FU) chemotherapy. We are concerned however about the conclusion reached by the authors and the accompanying commentary (Gut 2006;55:759–61) that MSI status should be considered in decisions on the use of 5-FU. While the clinical utility of MSI status for screening of hereditary non-polyposis colorectal cancer (HNPCC) is unquestioned, we are of the opinion that currently available data cannot justify exclusion of patients with MSI tumours from receiving 5-FU treatment.

The authors state that “5-FU based chemotherapy may not be useful in stage II and III MMR deficient colorectal cancer and a revision …