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.