225 Preoperative Magnetic Resonance Imaging for Decision Making Concerning Neoadjuvant Chemoradiation or Primary Surgery for Rectal Cancer. Interim Analysis of the German OCUM Trial (NCT01325649)

Abstract

Introduction: Total mesorectal excision (TME) surgery is the standard of care for rectal cancer. Neoadjuvant chemoradiation is frequently given in UICC II and III stages, although clinical TNM staging has limited accuracy. We aimed to prospectively evaluate the use of MRI with determination of circumferential margins (CRM) for decision making towards multimodal therapy. Methods: Multicenter prospective cohort study which enrolled 624 patients in 16 centers. Patients with T4 tumors or patients with a MRI circumferential margin of less than 1 mm were treated by neoadjuvant chemoradiation. All others went directly to surgery, except when the intersphincteric space appeared involved. Quality of TME and accuracy ofmrCRM determination compared to pathological workup (pCRM)were assessed. Results: TME was complete in 381 of 389 patients following primary surgery (97.9 %) and in 245 of 253 patients (96.8 %) after neoadjuvant chemoradiation. Negative pathological circumferential margins (pCRM negativ) were seen in 97.4 % after surgery without and in 89 % in patients after surgery following neoadjuvant chemoradiation. A negative pathological circumferential margin and mrCRM were in accordance in 98.3 % of rectal cancers. Neoadjuvant chemoradiation was given in 253 of 624 patients (39.8 %). Lymph node count was 23 (range 7-79; median/range) for primary surgery and 17 (range 2-56) for surgery following neoadjuvant chemoradiation. Conclusions: Surgical quality was excellent throughout the study. MRI based surgery allows to reduce the use of neoadjuvant chemoradiation avoiding its detrimental side-effects in many patients. Acknowledgments: This study is run by the OCUM study group in 16 centers in Germany / Switzerland