MRI-based indications for neoadjuvant radiochemotherapy in rectal carcinoma: interim results of a prospective multicenter observational study.

ABSTRACT

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.