Rectal Mucinous Adenocarcinoma: MR Imaging Assessment of Response to Concurrent Chemotherapy and Radiation Therapy-A Hypothesis-generating Study

Purpose: To develop a system for assessment of tumor regression grade (TRG) with magnetic resonance (MR) imaging that is applicable to rectal mucinous adenocarcinoma (RMAC) and to obtain a preliminary evaluation of the association of MR imaging assessment of TRG with response to preoperative concurrent chemotherapy and radiation therapy (CCRT). Materials and Methods: This retrospective study was approved by the institutional review hoard, and informed consent was waived. Pre- and post-C CRT MR images of 59 patients with RMAC (rneclian age, 59 years; range, 29-80 years; 42 men [median age, 59 years; range, 36-80 years] and 17 women [median age, 57 years; range, 29-79 years]) who underwent CCRT and subsequent elective resection front July 2005 to June 2015 were analyzed. Two experienced gastrointestinal radiologists independently analyzed imaging parameters such as T stage, mesorectal fascia status, extramural vascular invasion status, and TRG by using modified criteria developed for assessment of RMAC. Interobserver variability was calculated with weighted K analysis, and disagreement was settled in consensus. MR imaging TRG results were compared with those from pathologic TRG analysis (Manclarcl grade). Logistic regression analyses were performed to evaluate associations between imaging parameters and pathologic TRG. Results: There was moderate to substantial agreement for imaging parameters (post-CCRT T stage-weighted K, 0.7134; post-CCRT mesorectal fascia status. 0.618; TRG, 0.5023). Modified MR imaging TRG results were significantly associated with pathologic responsiveness (responsive group, Mandard grade 1 or 2; nonresponsive group, Manclard grades 3-5; P=.023). Results of univariate and multivariate logistic regression analyses indicated that MR imaging TRG was the only factor significantly associated with CCRT responsiveness (univariate analysis, P=.023; multivariate analysis. P =.0261). Conclusion: The modified MR imaging assessment of TRG was associated with treatment response to CCRT in patients with RMAC. (C) RSNA, 2017