Predictors and risk model for positive circumferential resection margin after robot-assisted total mesorectal excision: retrospective cohort study

Background: Positive circumferential resection margin (CRM) after total mesorectal excision (TME) is associated with higher local and systemic recurrence rates, affecting overall survival in patients with rectal cancer. Although risk factors for positive CRM have been identified for open, laparoscopic, and transanal TME, these may differ for robot-assisted total mesorectal excision (R-TME). This study aimed to assess the incidence of positive CRM following R-TME and identify the associated preoperative risk factors. Method: An international multicentre retrospective study included patients receiving R-TME between January 2013 and January 2022 in centres based in the Netherlands, UK, and France. Endpoints were the incidence of and predictive factors for positive CRM. Univariable and multivariable logistic regression analyses were performed, and factors associated with positive CRM were then assessed by formulating a predictive model. Results: A total of 1390 patients underwent R-TME, and the incidence of positive CRM was 6.0% (n = 83). Multivariable analysis revealed significant associations between positive CRM and cT4 tumours (OR 2.27), involved mesorectal fascia on staging magnetic resonance imaging at diagnosis (OR 1.89), and non-sphincter-saving surgery (OR 2.22). The predictive model exhibited satisfactory discrimination (area under the receiver-operating characteristic curve > 0.7) and predicted a 26% risk of positive CRM when all identified risk factors were present. Conclusion: Preoperative tumour- and procedure-related factors, rather than patient-related factors, are associated with CRM involvement after R-TME. The proposed predictive model allows preoperative calculation of the risk of positive CRM, offering valuable insights for optimizing patient selection and tailoring treatment approaches to enhance oncological outcomes.