Mismatch repair status in the prediction of benefit from adjuvant fluorouracil chemotherapy in colorectal cancer.

Some retrospective studies have shown a lack of benefit of 5-fluorouracil (5-FU) adjuvant chemotherapy in patients with mismatch repair (MMR) deficient colorectal cancer. Our aim was to assess if this molecular marker can predict benefit from 5-FU adjuvant chemotherapy. A second objective was to determine if MMR status influences short term survival. We included 754 patients with a median follow up of 728.5 days (range 1-1097). A total of 260 patients with stage II or III tumours received 5-FU adjuvant chemotherapy, according to standard clinical criteria and irrespective of their MMR status. A tumour was considered MMR deficient when either BAT-26 showed instability or there was loss of MLH1 or MSH2 protein expression. At the end of the follow up period, 206 patients died and 120 presented with tumour recurrence. Sixty six (8.8%) patients had MMR deficient tumours. There were no significant differences in overall survival (MMR competent 72.1%; MMR deficient 78.8%; p = 0.3) or disease free survival (MMR competent 61.3%; MMR deficient 72.3%; p = 0.08). In patients with stage II and III tumours, benefit from 5-FU adjuvant chemotherapy was restricted to patients with MMR competent tumours (overall survival: chemotherapy 87.1%; non-chemotherapy 73.5%; log rank, p = 0.00001). Patients with MMR deficient tumours did not benefit from adjuvant chemotherapy (overall survival: chemotherapy 89.5%; non-chemotherapy 82.4%; log rank, p = 0.4). Benefit from 5-FU adjuvant chemotherapy depends on the MMR status of tumours in patients with colorectal cancer. 5-FU adjuvant chemotherapy improves survival in patients with MMR competent tumours but this benefit from chemotherapy cannot be extended to patients with MMR deficient tumours.