T≤2N0 TRG1-2 in Post-Chemoradiation Therapy MRI: What can it Predict?

Total mesorectal excision is the standard radical operation after neoadjuvant chemoradiotherapy for patients with middle/low locally advanced rectal cancer. However, it carries significant rates of morbidity, sexual/urinary dysfunction, fecal impairment and permanent stoma. The ability to identify patients with a complete or nearly-complete response could help steer patients to less-invasive surgery or a watch-and-wait strategy.

To assess the ability to predict good responders and a favorable prognosis among rectal cancer patients by post-chemoradiation therapy MRI.

Consecutive patients stage T3-4N0M0 or T(any)N+M0 located within 10cm from the anal verge were enrolled. Patients were staged and re-staged 8.8 weeks after the completion of chemoradiation by digital exam, colonoscopy, pelvic-MRI, and thorax and abdominal CT scans. All patients underwent total mesorectal excision with curative intent.

Of the total 309 patients, 275 were eligible, and 199 (72.4%) of these were stage III. Restaging-MRI identified 59 (21.4%) T=2N0/TRG1-2. Specimen pathologic evaluation revealed 43 (15.6%) patients with a complete pathologic response. Estimates of the accuracy, sensitivity, specificity, positive predictive value, and negative predictive value of MRIyT=2N0/TRG1-2 for the identification of ypT0N0 were 79.7%, 84.5%, 53.5%, 39%, and 90.7%, respectively. Estimates for the identification of ypN0 were 48.4%, 27.8%, 92%, 88.1%, and 48.4%, respectively. In a multivariate analysis, the only pre-CRT/MRI variables that were associated with an increased risk of lymph node involvement at the specimen were N+ (OR=2.22) and extramural vascular invasion (OR=2.28). MRI yT=2N0/TRG1-2 patients showed improved estimated 5-year disease-free survival, but no difference in estimated 5-year survival.

Although MRIyT=2N0/TRG1-2 cannot predict all cases of a complete pathologic response, it can effectively predict a low rate of lymph node involvement and a better prognosis in patients who undergo total mesorectal excision.