Locally advanced rectal adenocarcinoma: Are preoperative short and long course radiotherapy truly equivalent?

Abstract

In the neoadjuvant treatment of locally advanced rectal adenocarcinoma, long- and short-course radiotherapy are considered to be of equivalent efficacy based upon several randomized trials. The present study assessed the effect of radiotherapy dose on overall survival. Using the National Cancer Database (2006-2013) 458 individuals with clinical stage II/III rectal adenocarcinoma treated were identified, with either short- (25 Gy) or long- (45 or 50.4 Gy) course neoadjuvant radiotherapy followed by surgery, without neoadjuvant or adjuvant chemotherapy. Multivariate COX regression was employed to evaluate differences in overall survival according to radiotherapy regimen. An association with improved overall survival in individuals treated with long- compared with short-course radiotherapy was demonstrated (HR=0.50, 0.34-0.73). The 30- and 90-day post-surgery mortality rates were higher in the short-course group when compared with the long-course group (12.2 vs. 2.4%; and 18.5 vs. 5.4%, respectively). Following the exclusion of patients that succumbed within 90-days post-surgery, overall survival advantage in the long-course group compared with the short-course group was maintained [hazard ratio (HR)=0.62, 0.39-0.99], with a median overall survival of 25.3 months (IQR 16.9-41.6) for the short-course group compared with 43.5 months (IQR 25.6-67.9) for the long-course group. To the best of our knowledge, the present results suggest for the first time that long-course radiotherapy is associated with an improved overall survival compared with short-course radiotherapy in locally advanced rectal adenocarcinoma in the absence of chemotherapy usage. This possible advantage is clinically relevant mainly in patients who cannot tolerate systemic chemotherapy.