Pelvic MRI for guiding treatment decisions in rectal cancer

Fluoropyrimidine-based chemoradiation (CRT) is used routinely for locally advanced rectal cancer to shrink the tumor preoperatively, improve lateral surgical clearance at total mesorectal excision, prevent local recurrence, and preserve organ function. In Northern Europe, short-course preoperative radiotherapy (SCPRT) is preferred to achieve locoregional control. However, with recent improvements in the quality of surgery, in magnetic resonance imaging (MRI), and in pathologic reporting, we question whether "routine" CRT or SCPRT should be offered indiscriminately for all patients.MRI is considered the optimal modality for locoregional staging and evaluation of the potential for an involved circumferential resection margin. MRI also provides detailed anatomic information for surgical planning, and may identify poor prognostic features, which influence the way in which the pathologist processes specimens. MRI can predict the likelihood of good/poor tumor response to neoadjuvant CRT and can categorize responders/nonresponders following treatment.Using MRI to define the risk of both local recurrence and metastatic spread allows clinicians to determine which patients might benefit from or safely avoid neoadjuvant treatment. We have arrived at these views after comparing data from published observational studies, results from randomized trials, and outcome analyses of the Norwegian National Cancer Registry.