Is There a Role for Perioperative Pelvic Radiotherapy in Surgically Resected Stage IV Rectal Cancer?

Objectives: This study aimed to determine whether perioperative pelvic radiotherapy (RT) improves outcomes in stage IV rectal cancer patients treated with primary surgical resection and systemic chemotherapy and to identify predictive factors for selection of patients for these approaches. Materials and Methods: We searched the Surveillance, Epidemiology, and End Results (SEER) database for patients diagnosed between 2010 and 2015 with stage IV rectal cancer, but without brain or bone metastases. After applying the exclusion criteria, a total of 26,132 patients were included in the analysis; propensity score matching was used to balance their individual characteristics. Results: Overall, 3283 (12.6%) patients received perioperative RT; the 3-year overall survival (OS) rates were 43.6% in the surgery group and 50.5% in the surgery with RT group ( P <0.001). The survival benefit of RT was maintained after propensity score matching and multivariate adjustment (hazard ratio: 0.70; 95% confidence interval: 0.66-0.81; P <0.001). Interaction testing of the prognostic variables showed a significant interaction between RT and the presence of lung metastasis ( P <0.001): the benefit of RT was observed only in patients without lung metastases (3 y OS 52.1% vs. 44.1%, P <0.001), but it was observed regardless of liver metastases. In addition, we developed a web-based calculator (http://bit.do/mRC_surv) to provide individualized estimates of OS benefit based on the receipt of perioperative pelvic RT. Conclusions: Perioperative pelvic RT significantly improved OS rates, especially in patients without lung metastases. We successfully developed a nomogram and web-based calculator that could predict survival benefit with the addition of RT for these patients.