Prediction of Occult Cervical Lymph Node Metastasis in Bone-Invasive pT4a cN0 Oral Squamous Cell Carcinoma in Relation to Tumor Size: A Retrospective Observational Cohort Study

<b>Objective:</b> The T classification of oral squamous cell carcinoma (OSCC) is linear according to the tumor size, excluding T4a by its criteria of invasion into adjacent structures, such as cortical bone. This may lead to the upstaging of otherwise small tumors. The objective was to analyze patients with OSCC and negative nodal staging to assess the impact of T-staging with tumor size on the incidence of occult cervical lymph node metastasis (CLNM) and regional neck failure. <b>Methods:</b> This retrospective cohort study included patients with OSCC and clinically negative necks (cN0), treated surgically between 2010 and 2024. All T4a OSCC classified due to bone invasion were additionally reclassified into T1-T3 based on size and depth of invasion according to the current staging manual. The primary endpoint of this study was the association between OSCC stratified by T-stage and tumor size as well as the presence of occult CLNM. <b>Results:</b> A total of 642 patients were included, with an overall occult CLNM rate of 20.2%. Bone invasion in T1-sized tumors was significantly associated with occult CLNM (OR 6.38, 95% CI: 1.48-27.42), whereas no such association was observed in T2 or T3 tumors (OR 0.80, 95% CI: 0.37-1.73; and OR 0.77, 95% CI: 0.37-1.62, respectively). Additionally, in T1-T2 tumors, bone invasion did not correlate with worse survival outcomes. <b>Conclusions:</b> Bone invasion was not significantly associated with occult CLNM in T2-3 sized OSCC, suggesting that the prognostic relevance is size-dependent. These findings question the uniform upstaging to T4a and support a more differentiated approach, potentially enabling neck management de-escalation in selected early-stage cases.