Prognostic performance of TNM8 staging rules in oral cavity squamous cell carcinoma

Background: Two major changes to the staging of oral cavity squamous cell carcinoma (OCSCC) were adopted in TNM8: (1) depth of invasion is now used for T staging and (2) extranodal extension for N staging. The aim of this study was to evaluate if TNM8 stratifies OCSCC patients more accurately than TNM7 based on overall survival (OS) statistics and hazard discrimination. Methods: Retrospective study of 297 patients with OCSCC who underwent surgery at our institution. Clinical and pathological data were previously populated from review of medical charts and histological reports. Slides were re-reviewed for depth of invasion measurements. Patients were staged using both TNM7 and TNM8 with overall survival statistics analysed. Results: Overall 118 patients (39.7%) were upstaged using TNM8. Both TNM7 and TNM8 stage categories were highly significant for OS (all p values < 0.0001). Hazard discrimination analysis showed that TNM7 could only differentiate stage III from stage IV disease with significance (OS p = 0.01). In comparison TNM8 could distinguish between stage II and III disease (OS p = 0.047) and between stage III and IV disease (OS p = 0.004). Subsite analysis suggested that both editions of the staging system perform best for tongue primaries. Conclusions: Although TNM8 showed improved hazard discrimination in comparison to TNM7, problems with discriminative ability persisted with 8th edition staging criteria. Large scale validation studies will be required to direct future refinement of the staging rules and to establish if the continued use of a single staging system for all oral cavity subsites is appropriate.