Colon cancer with DNA mismatch repair (MMR) defects reveals distinct clinical 
and pathologic features, including a better prognosis but reduced response to 
5-fluorouracil (5-FU)-based chemotherapy. A current standard treatment for 
recurrent or metastatic colon cancer uses capecitabine plus oxaliplatin (CAPOX), 
or continuous-infusion fluorouracil plus oxaliplatin (FOLFOX). This study 
investigated the effect of MMR status on the treatment outcomes for CAPOX and 
FOLFOX as first-line combination chemotherapy in recurrent or metastatic colon 
cancer. We analyzed 171 patients who had been treated with CAPOX or FOLFOX as 
first-line combination chemotherapy in recurrent or metastatic colon 
adenocarcinoma between February 2004 and July 2008. Tumor expression of the MMR 
proteins, MLH1 and MSH2, was detected by immunohistochemistry (IHC) in 
surgically resected tumor specimens. The microsatellite instability (MSI) was 
analyzed by polymerase chain reaction (PCR) amplification, using fluorescent 
dye-labeled primers specific to microsatellite loci. Tumors with MMR defect were 
defined as those demonstrating a loss of MMR protein expression (MMR-D) and/or a 
microsatellite instability-high (MSI-H) genotype. In all, 75 patients (44%) 
received FOLFOX, and 96 patients (56%) received CAPOX as first-line combination 
chemotherapy. The incidence of colon cancer with MMR defect was 10/171 (6%). 
Colon cancers with MMR defect (MSI-H and/or MMR-D) are more commonly located in 
proximal to the splenic flexure (p=0.03). The MMR status did not significantly 
influence the overall response (p=0.95) to first-line CAPOX or FOLFOX treatment 
in patients with recurrent or metastatic colon cancer. According to the MMR 
status, there was no significant difference for PFS (p=0.50) and OS (p=0.47) in 
patients with recurrent or metastatic colon cancer treated with first-line CAPOX 
or FOLFOX. In colon cancers with MMR defect, there was no significant difference 
for PFS (p=0.48) and OS (p=0.56) between CAPOX and FOLFOX as first-line 
combination chemotherapy. However, in MMR intact, there was significant 
difference for OS between CAPOX and FOLFOX (p=0.04). OS was significantly better 
in patients treated with CAPOX when compared to patients with FOLFOX. The MMR 
status does not predict the effect of oxaliplatin-based combination chemotherapy 
as 1st line in recurrent or metastatic colon cancers. CAPOX in the first-line 
treatment of recurrent or metastatic colon cancer with MMR intacts showed a 
superior OS compared with FOLFOX unlike colon cancer with MMR defects.