Metastatic characteristics associated with survival of synchronous metastatic nasopharyngeal carcinoma in non-epidemic areas

The current metastatic category (M) of nasopharyngeal carcinoma (NPC) is a "catch-all" category, we previously successfully established a M1 subdivision system based on prognostic metastatic characteristics in epidemic areas. We aimed to figure out metastatic characteristics associated with survival outcomes of NPC in non-epidemic areas. A total of 428 newly diagnosed de novo metastatic NPC patients from 2010 to 2016 were analyzed from the population-based Surveillance, Epidemiology, and End Results program. Cox proportional hazard ratios (HRs) were used to identify independent prognostic factors for survival. The most frequently involved metastatic locations were the bones (53.04%), the lungs (36.68%), the livers (29.21%) and the distant lymph nodes (24.07%). Univariate analysis indicated that bone involvement (HR = 1.39, 95% CI = 1.09–1.77), liver involvement (HR = 1.44, 95% CI = 1.12–1.85) and multiple metastatic locations (HR = 1.32, 95% CI = 1.04–1.67) were negative prognostic factors of overall survival (OS) for patients with synchronous metastasis. We established a new M1 subdivision system based on metastatic characteristics: M1a, without bone and liver involvement; M1b, single bone or liver involvement; M1c, multiple metastatic locations including bone and/or liver. Multivariate analysis confirmed that our new subcategories were associated with significantly different OS (M1b vs M1a: HR = 1.54, 95% CI = 1.11–2.16; M1c vs M1a: HR = 2.03, 95% CI = 1.47–2.78). Synchronous metastatic NPC patients with multiple metastatic locations involved bone and/or liver were prone to suffer from dismal OS and might need more attentions for selection of treatment modality.