JCOG-CCSG has been conducting several surgical trials and experienced several challenges. The first point is the appropriate timing of conducting the trial. Once a certain number of surgeons acquire the new technique and its utility is accepted, it suddenly becomes difficult to maintain 'equipoise' between the standard and new treatment, which may lead to poor patient accrual. Smooth preparation and commencement of the trial at an appropriate timing is necessary for its success. Second is the appropriate quality assurance of surgery. High-level quality assurance will strengthen the comparability of randomized control trials and minimize the heterogeneity among hospitals. On the other hand, it may impair the generalizability of the trial. Large observational studies help to bridge the gap of heterogeneity among hospitals. Third is the selection of an appropriate endpoint. Overall survival (OS) is the gold-standard primary endpoint; however, the number of events is much less due to more effective treatment. JCOG0212 and JCOG0404 were unable to demonstrate the non-inferiority of omission of lateral lymph node dissection and laparoscopic surgery partly due to a lack of power. Disease-free survival (DFS) is also a promising candidate for primary endpoint, but as in JCOG0603, special attention must be paid when DFS does not correlate with OS. Although careful discussion is required because the precision of the hazard ratio depends on the number of events, an alternative population-level summary of variables, including restricted mean survival time, can be considered as the primary endpoint. Future surgical trials should be planned considering these points.
Keywords: colon cancer; heterogeneity; rectal cancer; surgical trials.
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