Predicting Positive Radial Margin on Restaging MRI of Patients with Low Rectal Cancer: Can We Do Better?

Abstract Objective The aim of this study was to characterize the tissue involving margin and if information will affect prediction on restaging magnetic resonance imaging (MRI) in low rectal adenocarcinoma (LRC) patients treated with neoadjuvant long-course chemoradiotherapy (LCCRT). Methods In retrospective nonmetastatic LRC (distal <5 cm from anal verge) LCCRT followed by surgery, a radiologist blinded outcome reread MRI documented radial involved tumor, fibrosis, or mucin reaction using T2 high-resolution (HR) diffusion-weighted (DWI). diagnostic performance tumor-involving assessed surgical histopathology as reference. Interobserver agreement between three independent radiologists subset. Results We included 133 (80 males 53 females) mean (range) age 44.7 (21–86) years 82% them had well moderately differentiated adenocarcinoma. Baseline showed T3 (n = 58) T4 60) disease 89% patients. pathological positive 21% 28) cases. MRI, circumferential resection (CRM) ≤1 mm 75.1% 100) cases predicted at 60, 34, 6%, respectively, tumor cells 33, 14.7, 16.6% them, respectively. bad response (MR regression grade [mr-TRG] 3–5) fourfold increased risk (pCRM). There moderate fair inter-reader for type CRM (κ 0.471) mr-TRG 0.266), p < 0.05. use both distance criteria margins improved accuracy 39 66% MRI. Conclusions Margin can be characterizing cancer determining type.