Prognostic implications of the 8th edition American Joint Committee on Cancer (AJCC) staging system in oral cavity squamous cell carcinoma.

BACKGROUND: The American Joint Committee on Cancer (AJCC) has changed the staging system of oral squamous cell carcinoma (OSCC) in the 8th edition of its staging manual to include depth of invasion (DOI) of the primary tumor as a modifier to the T category and extranodal extension (ENE) to upstage node positive OSCC. This study aims to evaluate the performance of the AJCC 8 pathologic staging system in OSCC and compare it to its predecessor (AJCC 7).

METHODS: Analysis of 663 patients with OSCC from a prospective database was performed using the Cox proportional hazards competing risk model. The prognostic performance of the pathologic staging system was assessed using the Akaike Information Criterion (AIC) and Harrell's concordance index (C-index).

RESULTS: AJCC 8 led to upstaging of 35.6% (N = 235) of patients in this cohort. Both AJCC 7 and 8 show limited monotonicity and poor stratification between stage groups I to III. The estimates for model performance reveal that AJCC 8 has modest predictive capacity for overall survival (OS) and disease specific survival (DSS) (Harrell's C of 0.70 and 0.74, respectively) but is superior to AJCC 7 (Harrell's C of 0.65 and 0.69, respectively).

CONCLUSIONS: The AJCC 8 staging system is more complex than its former version due to the inclusion of DOI and ENE. Compared with AJCC 7, it performs better in stratifying survival of OSCC patients by stage.