Background: Less intensive regimens, focusing on survival and disease control, may be better first-line treatments in unresectable metastatic colorectal cancer (mCRC). Several randomized trials suggested that sequential cytotoxic agents in mCRC may improve overall survival compared with combination chemotherapy. This study investigated whether sequential treatment with Bmab-based first-line therapy with oxaliplatin has superior efficacy to combination treatment for unresectable mCRC. Methods: This study is a two-arm, multicenter, open-label, randomized phase III trial in Japan, comparing the efficacy and safety of sequential Cape/5-FU+Bmab with escalation to CapeOX/mFOLFOX6+Bmab versus combination CapeOX/mFOLFOX6+Bmab as the first-line treatment of mCRC. The primary endpoint is Time to failure of strategy (TFS). In the sequential arm (Arm A: oxaliplatin ‘wait-and-go’), treatment escalation from Cape/5-FU+Bmab to CapeOX/mFOLFOX6+Bmab is recommended for progressive disease. In the combination arm (Arm B: oxaliplatin ‘stop-and-go’), de-escalation from CapeOX/mFOLFOX6+Bmab to Cape/5-FU+Bmab is possible after 12 weeks of treatment. Re-escalation to CapeOX/mFOLFOX6+Bmab after progressive disease is considered only for patients who received de-escalation of oxaliplatin, not caused by oxaliplatin-associated toxicity, after 12 weeks of treatment. A target sample size of 304 evaluable patients is considered sufficient to detect a hazard ratio of 0.69 for the TFS of the sequential ‘wait-and-go’ approach compared with the combination ‘stop-and go’ approach with 80% power and a 2-sided significance level of 5%. From December 2014 to September 2016, 311 patients were enrolled across 81 centers in Japan. The follow-up period is until March 2018, and results are expected in 2019, and results are expected in 2019. Clinical trial information: 000015405.