Background: The results of IDEA collaboration study in ASCO 2017 suggested that adjusting the duration of adjuvant chemotherapy (CTx) for stage III colon cancer may be possible according to patient’s risk (T and N factors) and treatment regimen (FOLFOX and CAPOX) in order to balance the benefit and neurotoxicity of oxaliplatin-based CTx. The 12-Gene Assay Recurrence Score (12-gene RS), known as Oncotype DX, has been validated to predict the recurrence risk of stage II/III colon cancer patients through several studies, including our SUNRISE study (J Clin Oncol, 2016), and thus to personalize adjuvant CTx taking account of individual recurrence risk. The objective of this SUNRISE-DI study is to determine the impact of the 12-gene RS on adjuvant CTx treatment recommendations, including the decision for the duration of oxaliplatin-based CTx in stage III patients as well as that for oxaliplatin-based CTx versus 5FU-based monotherapy in stage II/III patients. This study enables us to evaluate how physicians employ the IDEA collaboration results combined with the 12-gene RS to determine the regimen. Methods: Patients who have a curatively resected Stage II/IIIA/IIIB colon cancer, an age of more than 20, and an ECOG PS of 0-1 are eligible. Treating physicians will formulate a treatment recommendation and complete a pre-assay questionnaire, and the 12-gene assay will be performed. Following receipt of the RS result, the treatment recommendation will be revised and a post-assay questionnaire completed. The primary endpoint is the proportion of changes in treatment recommendations between pre- and post-assay across all patients. Secondary endpoints include the proportion of changes by stage; the proportion of changes in the duration of oxaliplatin-based CTx (3 months vs 6 months); the proportion switched to observation only, 5-FU mono, or 5-FU plus oxaliplatin; and changes in expressed physician confidence level. The enrollment target is 200 patients with stage IIIA/IIIB and 100 patients with stage II from 15 centers in Japan. Clinical trial registry number: UMIN000028784