Challenges in the modification of the M1 stage of the TNM staging system for nasopharyngeal carcinoma: A study of 1027 cases and review of the literature

A series of modifications have been introduced to the TNM staging system over time for nasopharyngeal carcinoma (NPC), mainly focused on the T (primary tumor) and N (local node) components of the system. The M1 stage is a 'catch all' classification, covering a group of patients whose outlook ranges from potentially curable to incurable. Since the current M1 stage does not allow clinicians to stratify patients according to prognosis or guide therapeutic decision-making and allow comparison of results of radical and non-radical treatments, we aimed to subdivide the M1 stage according to a retrospective study of 1027 metastatic N PC patients and to review the relevant literature. Between 1995 and 2007, 1027 inpatients with distant metastasis from NPC were retrospectively analyzed. Various possible subdivisions of the M1 stage were considered, looking at different metastatic sites, the number of metastatic organs and the number of metastases. Survival rates were calculated using the Kaplan-Meier method and compared using the log-rank test. The most frequently involved metastatic sites were the bone, lung and liver. The incidence rates of solitary metastatic lesions and pulmonary metastasis were 16.2 and 41.3%. Despite the poor survival of these patients with a median survival of 30.8 months, patients in the metachronous metastatic group with metastases to the lung and/or solitary lesions, were defined as M la, and were significantly associated with favorable median survival of 41.5 and 49.1 months in the univariate and multivariate analysis, respectively. Patients in the metachronous metastatic group with metastasis to the lung and/or solitary lesions (M la) have a more favorable prognosis compared with those patients with multiple metastases located in other anatomic sites (M1b). These data, in one of the largest reported metastatic NPC cohorts, are the first to show the prognostic impact of metastatic status in NPC. As a powerful predictor, the potential clinical value of a modified M1 of the TNM system for NPC will facilitate patient counseling and individualize management.