Bone metastasis of esophageal carcinoma diagnosed as a first primary tumor: a population-based study

Background: This study aimed to explore predictors of bone metastasis (BM) of esophageal carcinoma (EC) and factors affecting the prognosis of EC with BM (ECBM). Methods: We retrospectively studied the data of EC patients from the Surveillance, Epidemiology, and End Results (SEER) database between 2010 and 2016. Logistic regression analysis was used to analyze the risk factors of BM. Cox regression and Fine and Gray's competing risk regression were performed to identify prognostic factors associated with all-cause and cancer-specific death, respectively. The Kaplan-Meier method was used to assess survival. Results: After exclusion, 8,916 patients were eligible, of whom 462 (5.2%) had ECBM. Independent risk factors of BM were age <65 years, male sex, stage T1, advanced N stage, and non-bone organ metastases. For EC, the median survival time (MST) was 17 months, and the 3-and 5-year survival rates were 31.6% and 23.3%, respectively; meanwhile, for BM, the MST was 5 months, and the 3-and 5-year survival rates were 2% and 1%, respectively. Adenocarcinoma, stage T2, the absence of non-bone organ metastases, and combined radiotherapy and chemotherapy were associated with a reduced risk of all-cause death in ECBM patients. Stage T2, the absence of non-bone organ metastases, and combined radiotherapy and chemotherapy were associated with a decreased risk of cancer-specific death in ECBM patients. Conclusions: Although rare, BM severely impairs the prognosis of EC. BM predictors and factors influencing the prognosis of ECBM may help distinguish high-risk patients with BM and assess survival in ECBM patients.