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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

Timothy Iveson, Rachel Kerr, Mark P. Saunders, Niels Henrik Hollander, Josep Tabernero, Andrew Mark Haydon, et al.

ABSTRACT

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.

All content © 2017 American Society of Clinical Oncology. All rights reserved.

Editorial comment from Prof Ducreux:
The aim of the IDEA initiative was to try to reduce the time of adjuvant chemotherapy after resection of a localized colon cancer. A consortium was created when it was considered that 6 countries were trying to launch or had already launched a trial raising this issue. These trials have some slight differences but their design was very common allowing putting together 12,834 patients to evaluate the ideal length of adjuvant chemotherapy of colon cancer.Despite this large number of patients, the results of the global analysis were not as clear as it was anticipated: the non-inferiority boundary was not reached for the global population of patients, however it was reached for Xelox (and not for Folfox), as it was reached too for T1-3 N1 tumors. These results could allow drawing the conclusion that Xelox 3 month is the best adjuvant treatment for these patients and that only pT4 and/or N2 patients should receive 6 months of treatment.  No difference between 6 and 3 months of treatment was reported in the Scottish trial including 6088 patients. On the other hand, the Italian trial did not confirm the non-inferiority of 3 months of Xelox or Folfox versus 6 months of treatment. Curiously this trial that included 3759 (two thirds of stage III, one third of stage II disease), showed rather worse results with 3 months of treatment in stage II patients. This result contradicts the idea that 3 months of treatment is sufficient for the less severe tumors…. Finally, the French trial including 2022 patients showed that 6 months of Folfox (only 10% of patients treated with Xelox) were superior to 3 months of treatment…..  At the end, it is not completely easy to give a conclusive advice that could be used in clinical practice. It has also to be kept in mind that the comparison between Xelox and Folfox was not the endpoint of these trials, even if it can be considered that in monotherapy capecitabine seemed to give better results that 5FU… At this stage, my recommendations would be to follow the results of the global analysis: 3 months of treatment for stage III “light” pT1-3N1, 6 months for pT4 or N2… And maybe it would be good to recommend a larger use of  Xelox regimen.… We are waiting for new presentations of more complete data during ESMO Madrid 2017….

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