The efficacy of postoperative radiotherapy for locally advanced rectal cancer without neoadjuvant therapy

Background: The 2018 guidelines for treatment of cancer by site recommended by the National Comprehensive Cancer Network (NCCN) does not include a specific treatment recommendation for rectal cancer patients who did not receive preoperative chemoradiotherapy. The study objective was to evaluate whether postoperative radiotherapy was effective for such patients. Methods: Survival was evaluated in 9,585 patients who underwent surgical resection for stage II or III rectal cancer and were registered in the Surveillance, Epidemiology, and End Results-Medicare database between 1992 and 2009. Overall survival (OS) benefit in propensity score (PS)-matched patient cohorts were estimated by Cox proportional hazards models. Results: After stratification by chemotherapy regimen, the difference in OS of stage III patients between the no-treatment and radiotherapy groups was significant (P<0.001). However, there was no significant difference in OS of stage III patients between 5-fluorouracil (5-FU) and 5-FU/radiotherapy groups (P=0.267). Also, the difference in OS between the FOLFOX and FOLFOX/radiotherapy groups was not significant (P=0.649). The PS-matching analysis confirmed aforementioned results. Conclusions: The evidence obtained in this study does not support postoperative radiotherapy for stage II rectal cancer or stage III patients who received postoperative chemotherapy. The use of postoperative radiotherapy for stage III patients who did not receive postoperative chemotherapy could increase OS.