Background: To evaluate the impact of primary tumor radiotherapy on survival in patients with unresectable metastatic rectal or rectosigmoid cancer.
Methods: From September 2008 to September 2017, 350 patients with unresectable metastatic rectal or rectosigmoid cancer were retrospectively reviewed in our center. All patients received at least 4 cycles of chemotherapy and were divided into two groups according to whether they received primary tumor radiotherapy. A total of 163 patients received primary tumor radiotherapy, and the median radiation dose was 56.69 Gy (50.4-60). Survival curves were estimated with the Kaplan-Meier method to roughly compare survival between the two groups. Subsequently, the 18-month survival rate was used as the outcome variable for this study. This study mainly evaluated the impact of primary tumor radiotherapy on the survival of these patients through a series of multivariate Cox regression analyses after propensity score matching (PSM).
Results: The median follow-up time was 21 months. All 350 patients received a median of 7 cycles of chemotherapy (range 4-12), and 163 (46.67%) patients received primary tumor radiotherapy for local symptoms. The Kaplan-Meier survival curves showed that the primary tumor radiotherapy group had a significant overall survival (OS) advantage compared to the group without radiotherapy (20.07 vs 17.33 months; P = 0.002). In this study, the multivariate Cox regression analysis after adjusting for covariates, multivariate Cox regression analysis after PSM, inverse probability of treatment weighting (IPTW) analysis and propensity score (PS)-adjusted model analysis consistently showed that primary tumor radiotherapy could effectively reduce the risk of death for these patients at 18 months (HR: 0.62, 95% CI 0.40-0.98; HR: 0.79, 95% CI: 0.93-1.45; HR: 0.70, 95% CI 0.55-0.99 and HR: 0.74, 95% CI: 0.59-0.94).
Conclusion: Compared with patients with stage IV rectal or rectosigmoid cancer who did not receive primary tumor radiotherapy, those who received primary tumor radiotherapy had a lower risk of death. The prescription dose (59.4 Gy/33 fractions or 60 Gy/30 fractions) of radiation for primary tumors might be considered not only to relieve symptoms improve the survival of patients with inoperable metastatic rectal or rectosigmoid cancer.
Keywords: Primary tumor radiotherapy; Propensity score matching; Stage IV rectal cancer.