Pretreatment high-resolution rectal MRI and treatment response to neoadjuvant chemoradiation

BACKGROUND: Use of rectal MRI evaluation of patients with rectal cancer for primary tumor staging and for identification for poor prognostic features is increasing. MR imaging permits precise delineation of tumor anatomy and assessment of mesorectal tumor penetration and radial margin risk. OBJECTIVE: The aim of this study was to evaluate the ability of pretreatment rectal MRI to classify tumor response to neoadjuvant chemoradiation. DESIGN: This study is a retrospective, consecutive cohort study and central review. SETTING: This study was conducted at a tertiary academic hospital. PATIENTS: Sixty-two consecutive patients with locally advanced (stage cII to cIII) rectal cancer who underwent rectal cancer protocol high-resolution MRI before surgery (December 2009 to March 2011) were included. MAIN OUTCOME MEASURES: The primary outcomes measured were the probability of good (ypT0-2N0) vs poor (≥ypT3N0) response as a function of mesorectal tumor depth, lymph node status, extramural vascular invasion, and grade assessed by uni- and multivariate logistic regression. RESULTS: Tumor response was good in 25 (40.3%) and poor in 37 (59.7%). Median interval from MRI to surgery was 7.9 weeks (interquartile range, 7.0 -9.0). MRI tumor depth was ^lt;1 mm in 10 (16.9%), 1 to 5 mm in 30 (50.8%), and >5 mm in 21 (33.9%). Lymph node status was positive in 40 (61.5%), and vascular invasion was present in 16 (25.8%). Tumor response was associated with MRI tumor depth (p = 0.001), MRI lymph node status (p < 0.001) and vascular invasion (p = 0.009). Multivariate regression indicated >5 mm MRI tumor depth (OR = 0.08; 95% CI = 0.01-0.93; p = 0.04) and MRI lymph node positivity (OR = 0.12; 95% CI = 0.03-0.53; p = 0.005) were less likely to achieve a good response to neoadjuvant chemoradiotherapy. LIMITATIONS: Generalizability is uncertain in centers with limited experience with MRI staging for rectal cancer. CONCLUSION: MRI assessment of tumor depth and lymph node status in rectal cancer is associated to tumor response to neoadjuvant chemoradiotherapy. These factors should therefore be considered for stratification of patients for novel treatment strategies reliant on pathologic response to treatment or for the selection of poor-risk patients for intensified treatment regimens.