Redefining the positive circumferential resection margin by incorporating preoperative chemoradiotherapy treatment response in locally advanced rectal cancer: A multicenter validation study

Purpose This study was conducted to validate the prognostic influence of treatment response among patients with positive circumferential resection margin for locally advanced rectal cancer. Materials and Methods Clinical data of 197 patients with positive circumferential resection margin defined as ≤ 2 mm after preoperative chemoradiotherapy followed by total mesorectal excision between 2004 and 2009 were collected for this multicenter validation study. All patients underwent median 50.4 Gy radiation with concurrent fluoropyrimidine based chemotherapy. Treatment response was dichotomized to good response, including treatment response of grade 2 or 3, and poor response, including grade 0 or 1. Results After 52 months median follow-up, 5-year overall survival (OS) for good responders and poor responders was 79.1% and 48.4%, respectively (p < 0.001). In multivariate analysis, circumferential resection margin involvement and treatment response were a prognosticator for OS and locoregional recurrence-free survival. In subgroup analysis, good responders with close margin showed significantly better survival outcomes for survival. Good responders with involved margin and poor responders with close margin shared similar results, whereas poor responders with involved margin had worst survival (5-year OS, 81.2%, 57.0%, 50.0%, and 32.4%, respectively; p < 0.001). Conclusion Among patients with positive circumferential resection margin after preoperative chemoradiotherapy, survival of the good responders was significantly better than poor responders. Subgroup analysis revealed that definition of positive circumferential resection margin may be individualized as involvement for good responders, whereas ≤ 2 mm for poor responders.