Rectal cancer treatment without neoadjuvant chemoradiation based on preoperative magnetic resonance imaging: Determinants of surgical quality in the German OCUM study.

526 Background: Preoperative chemoradiation adds functional impairment to patients undergoing total mesorectal excision (TME). Surgical quality is of paramount importance to achieve low local recurrence rates in patients operated without preoperative chemoradiation when a negative circumferential margin was shown by preoperative magnetic resonance imaging (MRI). We aimed to determine surgical quality in a prospective multicenter cohort study (OCUM) in patients selected by MRI for surgery without neoadjuvant chemoradiation. Methods: Quality of TME was assessed in three categories for 282 patients from 12 hospitals enrolled for surgery without preoperative chemoradiation (Nagtegaal et al. 2005, Quirke and Morris 2007). Tumor perforation, local tumor cell dissemination and number of lymph nodes were assessed. Further, negative predictive value of MRI for histopathological involvement of the circumferential margin was determined. Results: In patients undergoing TME the muscularis propria plane (category III) was reached in 1/282 patients (0,4 %). Intraoperative tumor cell dissemination was observed in 3/282 patients (1,1 %). Total number of lymph nodes was 25 (median, range 10-79) and 79/282 patients had positive lymph nodes (28 %). The number of 12 lymph nodes recommended by UICC was not reached in one patient. Preoperative MRI correctly predicted a negative circumferential margin involvement as determined by histopathological workup in 98,9 % of patients. Conclusions: Excellent results in terms of surgical quality are possible justifying surgery without pretreatment in patients with MRI-negative circumferental margin tumors. This concept avoids additional functional impairment and reduced quality of life following preoperative chemoradiation in selected patients. Clinical trial information: NCT01325649.