Comparison of the 8th edition of TNM staging of oral cancer with the 7th edition and its prognostic significance using clinical depth of invasion and extranodal extension

Abstract

Objectives: The 8th edition of the International Union Against Cancer Control/American Joint Committee on Cancer Staging System introduced depth of invasion (DOI) and extranodal extension (ENE) into the staging of oral cavity cancer. We evaluated the prognostic ability of this new staging system compared with the 7th edition using clinical DOI (cDOI) and clinical ENE (cENE).

Materials and methods: We retrospectively reviewed and restaged 2,118 patients with oral squamous cell carcinoma treated between 2001 and 2018 using cDOI and cENE. Overall and disease-specific survival were used as endpoints to compare the prognostic outcomes of the 7th and 8th editions using Harrell's concordance index (C-index).

Results: In total, 305 (14.4 %) cases were upstaged in the T category, 85 (4.0 %) cases were upstaged in the N category, and 280 (13.2 %) cases were upstaged in the overall TNM stage. The introduction of the cDOI increased the C-index and hazard ratio (HR) for each T category. The introduction of cENE increased the N3b category of 85 cases, bringing the total to 94 cases, thereby widening the differences between each N category. In the 8th edition, the C-index and HR for overall TNM stage increased, and the discrimination between stage groups improved.

Conclusions: The 8th edition of the TNM clinical staging system using cDOI and cENE predominantly identified patients with a high mortality rate, thus improving the ability to discriminate and prognosticate oral cancer.

Keywords: AJCC 8th edition; C-index; Clinical staging; DOI; Disease-specific survival; ENE; Head and neck cancer; Overall survival; TNM staging; UICC 8th edition.