Establishment and validation of M1 stage subdivisions for de novo metastatic nasopharyngeal carcinoma to better predict prognosis and guide treatment

•M1 stage could be subdivided into three categories (M1a, b, c).•The survival curves were distinctly separated among these three categories.•Loco-regional radiotherapy may benefit patients without liver involvement more (M1a, b).•The role of local treatment for metastases needs to be further examined.