MRI-Diagnosed Tumor Deposits and EMVI Status Have Superior Prognostic Accuracy to Current Clinical TNM Staging in Rectal Cancer

Background Data: MRI assessment of rectal cancer not only assesses tumor depth and surgical resectability but also extramural disease which affects prognosis. We have observed that nonnodal tumor nodules (tumor deposits; mrTDs) have a distinct MRI appearance compared to lymph node metastases (mrLNMs). Objective: We aimed to assess whether mrTDs and mrLNMs have different prognostic implications and compare these to other known prognostic markers. Methods: This was a retrospective cohort study of 233 patients undergoing resection for rectal cancer from January 2007 to October 2015. Data were obtained from electronic records and MRIs blindly rereported. Survival was determined using Kaplan-Meier method. Prognostic markers were evaluated using Cox regression and competing risks analysis. Inter-observer agreement for mrTD was measured using Cohen Kappa. Results: On multivariable analysis, baseline mrTD/mrEMVI (extramural venous invasion) status was the only significant MRI factor for adverse survival [hazard ratio (HR) 2.36 (1.54-3.61] for overall survival, 2.37 (1.47-3.80) for disease-free survival (both P < 0.001), superseding T and N categories. mrLNMs were associated with good prognosis (HR 0.50 (0.31-0.80) P = 0.004 for overall survival, 0.60 (0.40-0.90) P = 0.014 for disease-free survival). On multivariable analysis, mrTDs/mrEMVI were strongly associated with distant recurrence (HR 6.53 (2.52-16.91) P <= 0.001) whereas T and N category were not. In a subgroup analysis of posttreatment MRIs in postchemoradiotherapy patients, mrTD/mrEMVI status was again the only significant prognostic factor; furthermore those who showed a good treatment response had a prognosis similar to patients who were negative at baseline. Inter-observer agreement for detection of mrTDs was k0.77 and k0.83. Conclusions: Current MRI staging predicting T and N status does not adequately predict prognosis. Positive mrTD/mrEMVI status has greater prognostic accuracy and would be superior in determining treatment and follow-up protocols. Chemoradiotherapy may be a highly effective treatment strategy in mrTD/mrEMVI positive patients.