Role of Radiation Therapy in Liver-Only Oligometastatic Disease: A SEER Analysis

Abstract

Radiation therapy (RT) for oligometastasis has the potential to prolong survival in certain disease sites. There is a paucity of data regarding the benefit of RT for overall survival (OS) or disease-specific survival (DSS) in patients with liver-only oligometastatic disease. The Surveillance, Epidemiology and End Results Program (SEER) includes comprehensive metastasis data for patients from 2016-2019. The SEER database was queried for patients with liver-only metastatic disease at diagnosis by selecting stage IV cases with liver-only metastasis, without metastatic disease in bone, brain, lung, distant lymph nodes, or other sites. OS and DSS were estimated using Kaplan-Meier with log-rank analysis to compare patients who received RT versus no RT. Cox proportional hazards regression was applied to identify potential confounders. Subgroup analysis was used to explore the benefit of RT in different primary tumor sites including pancreas (N = 8846), followed by colon (N = 6535), lung (N = 3075), rectum (N = 1739), and stomach (N = 1448). A total of 29,422 patients with liver-only metastatic disease treated from 2016-2019 were included. The median age was 67 years old and 77.0% of the patients were Caucasian. 2448 (8.3%) patients were confirmed to have received RT. Patients who received RT had better OS (median survival, RT vs no RT: 18 vs 6 months, P<0.001) and DSS (18 vs 7 months, P<0.001). On multivariable analyses, RT still significantly improved both OS (HR: 0.705, 95% CI: 0.665-0.747, P<0.001) and DSS (HR: 0.390, 95% CI: 0.378-0.402, P<0.001) after adjusting for potential confounders, including age, tumor size, lymph node status, and chemotherapy. RT was significantly associated with improved OS and DSS (all P<0.001) in all primary tumors sites queried except for stomach primary for which RT did not impact OS (P = 0.122) and DSS (P = 0.229). In patients who received chemotherapy, RT also prolonged OS (P<0.001) and DSS (P<0.001). In the SEER database of patients with liver-only oligometastatic disease, RT improves OS as well as DSS, however the benefit varies for the different primary tumor sites. Prospective studies could help further clarify the survival benefits of RT in liver-only oligometastatic disease.