Tumor Depth of Invasion (Tumor > 4 cm/Depth > 10 mm and Depth > 20 mm) and Through Cortex/Skin Invasion are Both Valid Criteria for Classifying Tumors as pT4a in AJCC 2018 Oral Cavity Cancer Staging System.

BACKGROUND

According to the AJCC third to seventh edition staging manuals (1988-2010), the presence of through cortex and/or skin invasion in oral cavity squamous cell carcinoma (OCSCC) identifies T4a tumors. The AJCC eighth edition (2018) introduced a depth of invasion (DOI) > 20 mm as a criterion for pT4a. Subsequently, a revision maintained that tumors > 4 cm with a DOI > 10 mm should be classified as pT4a. We sought to analyze the prognostic impact of the three distinct criteria identifying pT4a disease.

METHODS

We examined 667 consecutive patients with pT3-4 buccal/gum/hard palate/retromolar SCC who underwent surgery between 1996 and 2016. pT1/pT2 (n = 108/359) disease were included for comparison purposes.

RESULTS

The 5-year outcomes of patients with pT1/pT2/without (n = 406)/with tumor > 4 cm/DOI > 10 mm (n = 261), pT1/pT2/DOI ≤ 20 mm (n = 510)/> 20 mm (n = 157), and pT1/pT2/without (n = 305)/with through cortex/skin invasion (n = 362) were as follows: disease-specific survival (DSS), 98%/89%/79%/65%, p < 0.001, 98%/89%/78%/59%, p < 0.001, and 98%/89%79%/69%, p < 0.001; overall survival (OS), 90%/79%/63%/51%, p < 0.001, 90%/79%/63%/42%, p < 0.001, and 90%/79%/65%/52%, p < 0.001. In pT3-4 disease, a tumor > 4 cm/DOI > 10 mm was an independent adverse prognosticator for 5-year DSS rate, DOI > 20 mm was an independent adverse prognosticator for 5-year DSS and OS rates, whereas through cortex/skin invasion independently predicted 5-year OS rates.

CONCLUSIONS

All of the three criteria (tumor > 4 cm/DOI > 10 mm, DOI > 20 mm, and through cortex/skin invasion) identify high-risk patients, which should be reflected in further revisions of pT4a classification in OCSCC.