Fig. 1
![Fig. 1](http://media.springernature.com/full/springer-static/image/art%3A10.1186%2Fs40880-017-0264-x/MediaObjects/40880_2017_264_Fig1_HTML.gif)
Kaplan–Meier distant metastasis-free survival curves for patients with N1 nasopharyngeal carcinoma stratified by a gross tumor volume of lymph node (GTVnd), b serum Epstein–Barr virus (EBV) DNA copy number, and c prognostic model. Low risk: EBV DNA ≤ 4000 copies/mL regardless of GTVnd; moderate risk: GTVnd ≤ 18.9 mL with EBV DNA > 4000 copies/mL; high risk: GTVnd > 18.9 mL with EBV DNA > 4000 copies/mL. DMFS distant metastasis-free survival