e14691 Background: pathologic response to neoadjuvant chemoradiation is a strong prognostic factor for rectal cancer. Some studies have suggesting a wait and see approach for rectal cancer after clinical complete response to chemoradiation. In this study, we tried to identify clinical predictive factors of pathologic response to neoadjuvant chemoradiation. Methods: we retrospectively reviewed data of 129 patients from a prospective database, treated between January, 2008 and December, 2012. Patients with mid and low rectal adenocarcinoma, clinically staged (MRI) as T3,T4 any N or any T, N+, received pre-operative chemoradiation, which consists in 5040 cGy, concomitant to 5-FU-based chemotherapy. All patients were operated, by radical TME procedures. The clinical variables analyzed were: age, gender, distance from dentate line, cT stage, cN stage, pre-treatment CEA level, NIH toxicity during chemoradiation, endoscopic assessment of response, and interval between the end of radiation and surgery. We investigate associations between these variables with complete pathological response (cPR) and “good” pathological response (gPR), defined as ypT0orT1 N0. Results: the rate of cPR was 20.2%. The rate of gPR was 31.8%. For predicting cPR, only the endoscopic assessment of response showed significant association with cPR. Among 18 patients with complete endoscopic response, 8 (44.4%) confirmed cPR after resection. Among 93 patients with endoscopic findings suggesting residual disease, 14 (15.1%) presented cPR (p=0.008). 55.6% (10/18) of patients with complete endoscopic response still have microscopic residual disease in the resected specimen. For predicting gPR, only the cN staging was significantly associated with ypT0orT1 N0 (23.9% of gPR among cN+ patients against 41.3% among cN0 patients; p=0.038). Conclusions: clinical tools are very poor for predicting pathological response to neoadjuvant chemoradiation therapy in patients with locally advanced rectal carcinomas. Despite endoscopic assessment of response by retoscopy have showed significant association with cPR, the predictive value was weak.
