Subclassification of skull-base invasion for nasopharyngeal carcinoma using cluster, network and survival analyses: A double-center retrospective investigation.

PURPOSE: To investigate the prognostic value of skull-base invasion (SBI) for nasopharyngeal carcinoma (NPC), propose a subclassification of SBI. METHODS: 792 and 433 patients with pathologically proven NPC and complete clinical and magnetic resonance imaging records at Sun Yat-sen University Cancer Center and Foshan Hospital were enrolled, and investigated using heat map/cluster, network and survival analyses. RESULTS: The results of heat map/cluster analyses and network analysis showed that T3 patients with pterygoid process and/or base of the sphenoid bone invasion (T3 slight) had better treatment outcomes than those with other SBIs (T3 severe). Significant differences were observed between T3-slight and T3-severe groups with regard to 5-year overall survival (OS) (93.0% vs. 83.5%, p = 0.014) and progression-free survival (PFS) (82.5% vs. 74.1%, p = 0.044) rates. No significant difference was observed between T3-slight group and T2 patients with regard to 5-year OS (93.0% vs. 84.7%, p = 0.062) and PFS (82.5% vs. 78.9%, p = 0.459) rates. Therefore, we downgraded patients with T3 slight to T2, yielding a new T classification sample. The survival curves of the 5-year OS and PFS rates of T2 and T3 were more reasonable after sample redistribution than those before sample redistribution. The differences in the 5-year OS and PFS rates between T2 and T3 patients after sample redistribution approached significance (p = 0.075 and 0.051, respectively). CONCLUSIONS: Different types of SBIs had different effects on the prognosis for NPC. We recommend patients with T3 slight not be defined as T3 but, rather, as T2.