• Kenichi Yoshimura, Keisuke Uehara, Yuichiro Tojima, Satoru Kawai, Yasuji Mokuno, Atsuyuki Maeda, Takanori Kyokane, Satoshi Kobayashi, Yuichiro Yoshioka, and Masato Nagino.
• Department of Clinical Trial Design & Management, Translational Research Center, Kyoto University Hospital, 54 Shogoin Kawahara, Sakyo, Kyoto, 606-8507, Japan. keyoshim@kuhp.kyoto-u.ac.jp
• Trials. 2013 Jan 1; 14: 17.

BackgroundAlthough, in Western countries, oxaliplatin-based regimens have been established as a gold standard treatment for patients with stage III or high risk stage II colon cancer after curative resection, in Japan fluorouracil-based regimens have been widely accepted and recommended in the guidelines for adjuvant settings in patients with stage III colon cancer. S-1, an oral preparation evolved from uracil and tegafur, has equivalent efficacy to uracil and tegafur/leucovorin for treating patients with advanced colorectal cancer and might be a suitable regimen in an adjuvant setting. However, the completion rate of the standard six-week cycle of the S-1 regimen is poor and the establishment of an optimal treatment schedule is critical. Therefore, we will conduct a multicenter randomized phase II trial to compare six-week and three-week cycles to establish the optimal schedule of S-1 adjuvant therapy for patients with stage III colon cancer after curative resection.Methods/DesignThe study is an open-label, multicenter randomized phase II trial. The primary endpoint of this study is three-year disease-free survival rate. Secondary endpoints are the completion rate of the treatment, relative dose intensity, overall survival, disease-free survival, and incidence of adverse events. The sample size was 200, determined with a significance level of 0.20, power of 0.80, and non-inferiority margin of a 10% absolute difference in the primary endpoint.DiscussionAlthough S-1 has not been approved yet as a standard treatment of colon cancer in an adjuvant setting, it is a promising option. Moreover, in Japan S-1 is a standard treatment for patients with stage II/III gastric cancer after curative resection and a promising option for patients with colorectal liver metastases in an adjuvant setting. However, a six-week cycle of treatment is not considered to be the best schedule, and some clinicians use a modified schedule, such as a three-week cycle to keep a sufficient dose intensity with few adverse events. Therefore, it will be useful to determine whether a three-week cycle has an equal or greater efficacy and tolerance to side-effects compared with the standard six-week cycle schedule, and thus may be the most suitable treatment schedule for S-1 treatment.Trial RegistrationThe University Hospital Medical Information Network (UMIN) Clinical Trials Registry UMIN000006750.

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