Diffusion-weighted magnetic resonance imaging of mucin pools in locally advanced rectal mucinous adenocarcinoma predicts tumor response to neoadjuvant therapy.

PURPOSE: To determine the prognostic value of diffusion-weighted magnetic resonance imaging (DW-MRI) of mucin pools (MPs) in predicting the response of patients with locally advanced rectal mucinous adenocarcinoma (RMAC) to neoadjuvant therapy (NAT).

METHOD: A total of 59 patients with histologically proven RMAC received NAT before applying total mesorectal excision. MP and solid tumor (ST) components were identified using T2 weighted image (T2WI) and DW-MRI, and apparent diffusion coefficient (ADC) values were calculated prior, during and after NAT. The receiver operating characteristic (ROC) curve was used to evaluate the ability of ADC values in predicting NAT efficacy as determined by post-pathological tumor regression grade (TRG). In addition, radiologists evaluated the TNM staging of tumors, the mesorectal fascia invasion, the maximal tumor length, and the distance from the inferior part of the tumor to the anal verge. Multivariate analysis and logistic regression were used to determine the correlation of ADC values and baseline MRI parameters with NAT efficacy.

RESULTS

Among the 59 patients, 44 (74.6 %) were men. The mean age of patients was 49.5 ± 11.2 years. The mean ΔADC value during NAT obtained on mucus pool was higher in the responsiveness group than that of the nonresponsiveness group (0.506 ± 0.342 vs. 0.053 ± 0.240 × 10-3 mm2/s, P < .001), with an area under the curve of receiver operating characteristic of 0.881 (95 %CI, 0.770-0.951).

CONCLUSIONS

MRI can be reliably used to measure MP-ADC, which as we showed in this study, represents a biomarker to predict tumor responsiveness of NAT in RMAC patients.