Palliative beam radiotherapy offered real-world survival benefit to metastatic rectal cancer: A large US population-based and propensity score-matched study.

Purpose: Radiotherapy (RT) has been reported to effectively palliate many symptoms of patients with metastatic rectal cancer (mRC). The objective of this study was to evaluate the survival benefit of RT in mRC. Methods: A retrospective population-based cohort study was performed using the Surveillance, Epidemiology, and End Results Program (SEER) database. Patient baseline demographic characteristics between the RT and no-RT groups were compared using Pearson chi-square tests. The outcome of interest was cause-specific survival (CSS). Propensity score (PS) matching and Cox proportional hazards regression analyses were performed to evaluate the prognostic power of variables on CSS. Results: A total of 8851 patients with mRC were identified in the SEER database. Multivariable Cox regression analysis showed that RT was a protective factor in mRC (hazard ratio [HR]= 0.702, 95% confidence interval [CI]=0.665-0.741, p<0.001). In subgroup analysis, multivariate Cox analysis demonstrated that patients of both surgery and no-surgery subgroups treated with RT had better CSS than those not treated with RT (HR=0.654, 95%CI=0.607-0.704, p<0.001 for the surgery group; HR=0.779, 95%CI=0.717-0.847, p<0.001 for the no-surgery group), PS matching resulted in 4170 mRC patients and RT group presented significantly improved survival benefit than no-RT group (22.0 vs. 13.5%, P <0.001). In surgery subgroup after PS matching, in especial, RT group showed more evidently improved survival benefit than no-RT group (30.3 vs. 18.0%, p <0.001). Conclusion: Using the SEER database, we definitely demonstrated that RT was associated with a significant survival advantage beyond the relief of a variety of pelvic symptoms in the setting of mRC. This study strongly supports the use of RT in selected patients with mRC, especially in patients who have undergone surgery. More studies need to be conducted to accurately define the role of RT in mRC.