The significance of the depth of invasion and tumor size in resected pathologic T4a gingivobuccal squamous cell carcinoma

Oral cavity squamous cell carcinoma (SCC) is the most common head and neck region tumor. The pathologic T4a classification is defined tumor invasion by three distinctive subgroups with skin, bone marrow, or a depth of invasion (DOI) > 10 mm and tumor size > 40 mm, as specified in the revised AJCC 8th edition staging manual. We examined these three subgroups' different survival outcomes and explored factors influencing survival in patients with pT4a gingivobuccal SCC, and further investigate the discriminatory capacity among these three subgroups. All patients (n = 120) were treated from January 2010 to December 2021 for pT4a gingivobuccal SCC. Sixty-six (55%) exhibited bone invasion, 62 (51.7%) had skin invasion, and 44 (36.7%) had a deep DOI (DOI > 10 mm and tumor size > 40 mm). The median follow-up period for all patients was 93.6 months. The median overall survival (OS) was 48.1 months for patients with shallow (≤ 10 mm) vs. 25.1 months for those with deep DOIs (p = 0.03). The study found that deep DOI tumors were the primary factor influencing poorer OS in patients classified as pT4a after conducting a subgroup analysis. Three independent factors predicted poor prognosis: deep DOI (hazard ratio [HR] = 2.08, 95% confidence interval [CI] 1.00-4.31), extranodal extension (HR = 2.35, 95% CI 1.16-4.79), and positive resection margin (HR = 2.96, 95% CI 1.14-17.73). Deep DOI predicted worse outcomes and outperformed the risks of bone/skin invasion among these patients with pT4a gingivobuccal SCC.