Abstract
IMPORTANCE: Oral cavity squamous cell carcinoma (SCC) tumors with mandibular invasion are upstaged to pT4a regardless of their size. Even small tumors with boney invasion, which would otherwise be classified as pT1-2, are recommended for the locally advanced treatment pathway to receive administration of postoperative radiotherapy (PORT). OBJECTIVE: To evaluate the association of PORT with overall survival according to tumor size among patients who received mandibulectomy for pT4aN0 oral cavity SCC. DESIGN, SETTING, AND PARTICIPANTS: This was a retrospective analysis using data from the US National Cancer Database from January 1, 2004, through December 31, 2019. All patients who received mandibulectomy for treatment-naive pT4aN0 oral cavity SCC with negative surgical margins were included. Data analyses were performed in January 2023 and finalized in July 2023. EXPOSURE: PORT vs no PORT. MAIN OUTCOMES AND MEASURES: Entropy balancing was used to balance covariate moments between treatment groups. Weighted multivariable Cox proportional hazards regression was used to measure the association of PORT with overall survival associated with tumor size. RESULTS: Among 3268 patients with pT4aN0 oral cavity SCC (mean [SD] age, 65.9 [12.1] years; 2024 [61.9%] male and 1244 [38.1%] female), 1851 (56.6%) received PORT and 1417 (43.4%) did not receive PORT. On multivariable analysis was adjusted for age, insurance status, Charlson Comorbidity Index score, tumor site, tumor grade, tumor size, and PORT. Findings indicated that PORT was associated with improved overall survival and that this relative survival advantage trended upwards with increasing tumor size. That is, the larger the tumor, the greater the survival advantage associated with the use of PORT. For the 1068 patients with tumors greater than 4 cm, the adjusted hazard ratio (aHR) in favor of PORT was 0.63 (95% CI, 0.48-0.82); for the 1774 patients with tumors greater than 2 cm but less than or equal to 4 cm, the aHR was 0.76 (95% CI, 0.62-0.93); and for 426 patients with tumors less than 2 cm, the aHR was 0.81 (95% CI, 0.57-1.15). CONCLUSIONS AND RELEVANCE: In this retrospective analysis of patients who received mandibulectomy for pT4aN0 oral cavity SCC, PORT was associated with improved overall survival, the benefit of which improved relatively with increasing tumor size. These findings suggest that tumor size should be considered in guidelines for PORT administration in this patient population.