This is a randomized, multicenter study designed to evaluate the progression free survival of the SOL group (S-1, Leucovorin, and Oxaliplatin) compared with the mFOLFOX6 group (5-FU, l-LV and Oxaliplatin) as first-line treatment of patients with metastatic colorectal cancer.

Inclusion Criteria:

• Histologically proved adenocarcinoma (colorectal cancer).
• Age: 20 ≤ at enrollment.
• No prior treatment (ex. radiation therapy, chemotherapy, hormonal therapy) to advanced disease. Patients who received adjuvant chemotherapy more than 180 days before enrollment can be allowed but those who received S-1 or Oxaliplatin containing treatment shall be excluded.
• At least one measurable lesion by RECIST criteria

Exclusion Criteria:

• Serious drug hypersensitivity.
• Prior history of peripheral neuropathy.
• Diarrhea .
• Simultaneously active double cancer.