An update on rectal cancer evaluation by magnetic resonance imaging in neoadjuvant therapy decision making: Retrospective case review.

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762 Background: During the last decade, MRI used for staging of rectal cancer has been reported to up or down stage rectal cancer by 20%. Poor staging affects guided pre-operative decision-making. Adequate staging would enable to stratify treatment, avoiding unnecessary surgical morbidity and allowing aggressive interventions according to patient risk. After novel techniques and image acquisition for MRI became available at our Cancer Center, we aimed to analyze perfusion pattern and qualitative T2 signal before and after chemoradiationtherapy (CRT) tumor response to the gold standard pathological stage. Methods: Data was retrospectively reviewed from our institution cancer registry. Patients were selected with a diagnosis of rectal cancer by biopsy, between 2011-2015. Inclusion criteria were to have documented radiological AJCC 7th edition < IV, accessible diffusion weighted MRI for apparent diffusion coefficient analyzes, completed CRT and pathology report. Results: A total of 57 patients were diagnosed with rectal cancer during this time period, of which 20 fulfilled inclusion criteria; median 61 years old, 80% males, stage IIA (6) IIIB (10) and IIIC (4), LAR 60% and APR 40%. After CRT, 90% of patients (N18) were downstaged (and 2 upstaged) on pathological review. 10 patients had a repeat pre-operative MRI. Post-treatment MRI re-stage correlated with surgical pathological stage in all 10 patients (Table). 4 patients received unnecessary APR and 2 may had benefit from further CRT or total pelvic exanteration. Conclusions: In retrospective, tumor response evaluation post CRT with high-resolution MRI correlated with pathological stage. Our analysis pointed 20% patients may avoid a morbid surgery while 10% would have required more aggressive therapy. Future clinical decisions will be complemented by repeat MRI analysis aiding surgical and clinical decision-making. [Table: see text]