The effect of primary tumor radiotherapy in patients with Unresectable stage IV Rectal or Rectosigmoid Cancer: a propensity score matching analysis for survival

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.