Adjuvant Radiotherapy Is Not Necessary for Stage III Mucinous Rectal Cancer: Evidence Based on Long Survival Analysis from SEER Data

Background Although rectal mucinous adenocarcinoma (RMC) is less sensitive to radiotherapy, adjuvant radiotherapy is still recommended for RMC patients. This study aimed to explore whether adjuvant radiotherapy is necessary for stage III RMC. Methods Data of patients with stage III RMC were obtained from the National Cancer Institute’s SEER database (2004–2015). The survival rates were calculated by Kaplan–Meier method and compared by log-rank test. Univariate and multivariate Cox regression analyses were used to assess the impact of clinicopathological parameters on overall survival (OS) and cancer-specific survival (CSS). Results RMC has a worse T and N stage at diagnosis than rectal adenomatous carcinoma (RAC) (all p < 0.001). Multivariate Cox regression analyses revealed that histopathological type MC was an independent poor prognostic factor for OS (HR 1.27; 95%CI 1.14–1.41; p < 0.001) and CSS (HR 1.34; 95%CI 1.18–1.51; p < 0.001). Subgroup analysis based on different treatment regimens showed no significant difference between chemotherapy group and chemotherapy plus radiotherapy group. After the propensity score matching, no significant difference was also found in OS and CSS between chemotherapy group and chemotherapy plus radiotherapy group. Conclusions RMC is an independent poor prognostic factor for OS and CSS. Adjuvant radiotherapy for RMC was not beneficial in improving survival outcomes.