Final DFS results of the SCOT study: An international phase III randomised (1:1) non-inferiority trial comparing 3 versus 6 months of oxaliplatin based adjuvant chemotherapy for colorectal cancer

3502 Background: Six months of oxaliplatin-based treatment has been the mainstay of adjuvant chemotherapy for colorectal cancer for the last 13 years. Neurotoxicity from oxaliplatin is cumulative, dose limiting, and potentially irreversible. A shorter duration of treatment would save patients significant toxicity/time and substantially reduce the costs of the drug, its administration, and treatment of adverse effects. Methods: SCOT is a non-inferiority randomised study designed to determine whether 3 months of adjuvant chemotherapy with OxMdG or Xelox (physician/patient choice) in Stage III/high risk Stage II colorectal cancer is as effective as 6 months treatment. Non-inferiority was determined to be a maximum 2.5% fall in 3-year disease-free survival (DFS) on the 3 month arm (from 78% on the 6 month arm) corresponding to a hazard ratio upper limit of 1.13. The study was designed with 90% power at the 2.5% 1-sided level of statistical significance and aimed to recruit 9500 patients to observe 2,750 DFS events (relapses/deaths/new colorectal cancers). Analysis used a Cox model adjusted for study minimisation factors. Results: 6088 patients (60% male, median age 65) with Stage III/high risk Stage II cancers of the colon or rectum were randomised between 27th March 2008 and 29th November 2013. The arms were balanced for clinical and pathological factors. Intended treatment was OxMdG for 1981 and Xelox for 4107 patients. There were 1469 DFS events (734 in 3 month arm and 735 in 6 month arm) giving the study 66% power. 3 year DFS was 76.8% (se = .8%) for the 3 month arm and 77.4% (se = .8%) for the 6 month arm (HR 1.008, 95% CI 0.910-1.117, test for non-inferiority p = 0.014). Non-inferiority appeared stronger for Xelox than OxMdG (test for heterogeneity, p = .059). Results will be shown broken down by stage, site, age, gender and achieved duration of treatment. Conclusions: The SCOT study has shown that 3 months adjuvant treatment is not inferior to 6 months treatment. However the SCOT study is part of the IDEA consortium and the results from the 6 studies in the IDEA consortium addressing the same duration question will also be presented at ASCO 2017. Clinical trial information: ISRCTN59757862.