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

Introduction: 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.

Methods: 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.

Results: 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).

Conclusions: 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.