The role of adjuvant radiotherapy in relation to tumor size for bone-invasive pT4aN0 oral squamous cell carcinoma - A retrospective observational matched cohort study.

Objective: Oral squamous cell carcinoma (OSCC) with bone invasion are staged as pT4a, potentially upstaging smaller tumors. This study aimed to evaluate the oncological benefit of postoperative radiotherapy (PORT) in pT4aN0 OSCC with respect to tumor size and without other risk factors.

Methods: This retrospective matched cohort study included pT4aN0 OSCC patients with bone invasion treated surgically (R0) between 2010 and 2022. Each case was 1:1 matched to a pT1-3 N0 OSCC patient based on tumor size, but without bone invasion. The primary endpoint was overall survival (OS), secondary endpoints included the recurrence-free survival and outcome predictors.

Results: A total of 156 patients were analyzed (78 per group). There were no statistically significant differences in 3-year OS between both groups in general (78.2%, 95%CI: 68.6-87.8 vs. 80.0%, 95%CI: 68.4-91.6). After stratification for pT2 criteria, there was also no significant difference between both groups if PORT was omitted (63.9%, 95%CI: 44.2-92.4 vs. 70.5%, 95%CI: 55.0-90.0). Multivariate analysis identified age and poor differentiation (grade III) as significant predictors of worse OS, while PORT showed no independent survival benefit.

Conclusion: In small OSCC staged pT4a due to bone invasion and lacking other risk factors, PORT demonstrated no statistically significant improvement in OS when matched for tumor size. Further prospective trials and larger cohorts are warranted to confirm these findings.