Predictive factors of positive circumferential resection margin after radiochemotherapy for rectal cancer: the French randomised trial ACCORD12/0405 PRODIGE 2

Circumferential resection margin (CRM) appears as a new powerful prognostic factor of survival after surgery for rectal cancer. We aimed to evaluate predictive factors of positive CRM following preoperative radiochemotherapy in a French trial. Patients with rectal cancer were randomised in long course preoperative radiotherapy 45 Gy plus capecitabine versus 50 Gy plus capecitabine and oxaliplatin. Mesorectal excision was performed 6 weeks after treatment. Impact of clinical, pathological and surgical variables on positive CRM (≤1 mm) were analysed by multivariate analysis. Of 565 randomised patients, CRM was recorded in 390 cases and was positive in 8% (30/390). Patients with 50 Gy plus capecitabine and oxaliplatin had a 6% rate of positive CRM while those treated by 45 Gy plus capecitabine had a 10% rate (p=0.128). Three independent predictive factors of positive CRM were identified: abdominoperineal resection (APR) (odds ratio OR=3.24; p=0.004), vascular tumour invasion (OR=2.78; p=0.026) and poor histological response (modified Dworak 0-2) (OR=9.01; p=0.003). Significant predictive factors of positive CRM are related to type of surgery, especially APR, and poor histological prognostic factors. Intensification of neoadjuvant radiochemotherapy does not seem to have a major role in this study.