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.
To evaluate the ability of pre-treatment rectal MRI to classify tumor response to neoadjuvant chemoradiation.
Retrospective, consecutive cohort study, central review.
Tertiary academic hospital.
62 consecutive patients with locally advanced (stage cII-cIII)rectal cancer who underwent rectal cancer protocol high resolution MRI prior to surgery(12/09-3/11).
Main Outcome Measures
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 multi-variate logistic regression.
Tumor response was good in 25, 40.3% and poor in 37, 59.7%.Median interval from MRI to OP was 7.9weeks (IQR: 7.0–9.0). MRI tumor depth was <1 mm in 10 (16.9%), 1–5 mm in 30 (50.8%), and >5 mm in 21(33.9%). LN 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 nodes status (P=<0.001)and vascular invasion (P=0.009). Multivariate regression indicated >5mm MRI tumor depth (OR=0.08, 95% CI=0.01–0.93, p=0.04) and MRI LN positivity (OR=0.12, 95% CI=0.03–0.53, p=0.005) were less likely to achieve a good response to neoadjuvant chemoradiotherapy.
Uncertain generalizability in centers with limited experience with MRI staging for rectal cancer.
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.