Fig. 4

Kaplan-Meier survival estimates for NPC patients according to two different staging systems. In all, 3814 (63.2%) NPC patients from mainland China were diagnosed before 2006 and were staged according to the 1992 China staging system, whereas 2217 (36.8%) from Hong Kong, Taiwan, Singapore, and SYSUCC (in mainland China) were diagnosed between 2007 and 2011 and were staged according to the 1997 AJCC staging system. The 5-year OS rate was 69.2% (95% CI = 67.7%–70.6%) for patients classified by the 1992 China staging system (a) and 82.2% (95% CI = 80.3%–83.9%) for patients classified by the 1997 AJCC staging system (b). The OS differed significantly by clinical stage according to the 1992 China staging system (P < 0.001, c) and the 1997 AJCC staging system (P < 0.001, d). The log-rank test was used to calculate P values