Survival outcomes in unresectable metastatic rectal cancer patients after both primary site resection and chemoradiotherapy: a SEER-based observational study

BACKGROUND: The liver is the most common site for rectal cancer metastasis, and liver resection combined with chemotherapy is the only treatment offering the possibility of long-term survival in patients with metastatic rectal cancer. However, a significant proportion of liver metastases cannot be surgically removed, and very limited data are available regarding the survival outcomes of these patients. This study aimed to investigate the survival pattern of rectal cancer patients with unresectable liver metastases after both chemoradiotherapy and primary tumor resection. METHODS: A total of 51,178 rectal cancer patients were identified from the Surveillance, Epidemiology, and End Results (SEER) database, of whom 448 had synchronous liver metastases and underwent both chemoradiotherapy and primary tumor resection. According to different treatment modalities, patients were divided into a hepatic resectable group and an unresectable group. The Kaplan-Meier method was used to estimate patient survival, and differences between the hepatic resectable and unresectable groups were compared using the log-rank test. Univariate and multivariate Cox regression models were used to analyze independent prognostic factors for unresectable tumors. RESULTS: Among the 448 metastatic rectal cancer patients, 60.3% (270) had unresectable liver metastasis. The median survival period, 2-year overall survival (OS) rate, and 5-year OS rate of the unresectable group were 37.0 months, 68.5%, and 32.9%, respectively, compared with 56.0 months, 87.4%, and 48.0%, respectively, in the hepatic resectable group (P<0.001). Multivariate Cox regression analysis suggested that a poor or undifferentiated histological type was independently associated with poor CSS in patients with unresectable liver metastases (P=0.001). CONCLUSIONS: Primary tumor resection combined with chemoradiotherapy might be able to yield a satisfactory survival outcome in unresectable metastatic rectal cancer patients. Resection of liver metastases remains the primary treatment for prolonging the OS and CSS time in stage IV patients.