MRI-Based Indications for Neoadjuvant Radiochemotherapy in Rectal Carcinoma: Interim Results of a Prospective Multicenter Observational Study

Background This study evaluated use of circumferential resection margin status in preoperative MRI (mrCRM) as an indication for neoadjuvant radiochemotherapy (nRCT) in rectal carcinoma patients. Materials and Methods In a multicenter prospective study, nRCT was given to patients with carcinoma of the middle rectum with positive mrCRM (≤1 mm), with cT3 low rectal carcinoma, and all patients with cT4 tumors. The short-term endpoints were pathologic pCRM (≤1 mm) as a strong predictor of local recurrence rate and the quality of total mesorectal excision according to the plane of surgery. These endpoints were compared in patients with and without nRCT. Results Of 230 patients that met the inclusion criteria, 96 (41.7%) received a long course of nRCT and 134 (58.3%) were primarily operated on. The pCRM was positive in 13 of 230 (5.7%) (primarily operated on, 2 of 134 [1.5%]; after nRCT, 11 of 96 [11%]). In 1 of 134 (0.7%) case, the mrCRM was falsely negative. Patients at participating centers varied in terms of preoperative stage but not in pCRM positivity (0%–13%, P = .340). The plane of surgery was mesorectal (good) in 209 of 230 (90.9%), intramesorectal (moderate) in 16 of 230 (7%), and the muscularis propria plane (poor) in 2.2% (5 of 230). Conclusions Low pCRM positivity and the high quality of mesorectal excision support use of MRI-based nRCT in rectal carcinoma. nRCT was avoidable in 45% of patients with stage II and III disease without significant risk of undertreatment. Preoperative MRI thus allows identification of patients with high risk of local recurrence and use of selective nRCT.