Evaluating depth of invasion across oral cavity subsites as part of the AJCC 8th edition T staging criteria for oral cavity squamous cell carcinoma

Background: The prognostic impact of depth of invasion (DOI) in American Joint Committee on Cancer 8th edition TNM staging for oral cavity squamous cell carcinoma (OCSCCa) across oral cavity subsites is unknown. Methods: Overall survival of patients with pT1-4a OCSCCa in the National Cancer Database (2010–2017), stratified by tumor size and DOI across eight oral cavity subsites, was evaluated using multivariable-adjusted Cox proportional hazards modeling. Results: When stratified by tumor size ≤2 cm and >2 cm, DOI >5 mm and DOI >10 mm were only associated with worse overall survival, respectively, for tumors of the oral tongue (Tumor size ≤2 cm, DOI >5 mm v DOI ≤5 mm: HR: 1.31, 95% CI: 1.12–1.53, p < 0.001; Tumor size >2 cm, DOI >10 mm v DOI ≤10 mm: HR: 1.15, 95% CI: 1.01–1.30, p = 0.03). DOI >5 mm and DOI >10 mm was not prognostic for any other tumor location. Conclusions: These findings suggest that the current staging schema for DOI in OCSCCa may not be prognostic across all oral cavity subsites.