Adjuvant radiotherapy mitigates impact of perineural invasion on oncologic outcomes in early-stage oral cavity squamous cell carcinoma. A multi-institutional analysis of 557 patients

Objectives: Understand the prognostic impact of perineural invasion (PNI) in early-stage oral cavity squamous cell carcinoma (OCSCC). Assess the influence of adjuvant radiotherapy on outcomes of patients with PNI-positive early-stage OCSCC. Materials and Methods: Retrospective seven-institution cohort study including patients with pathologic T1-2 N0-1 OCSCC who underwent primary surgery with negative margins. Outcomes included disease-free survival (DFS) and locoregional control (LRC). Cox proportional hazards models were used to evaluate oncologic outcomes. Interaction terms were introduced to assess relationships between PNI and adjuvant radiotherapy. Results: Among 557 patients (mean (SD) age 61.0 (13.9), 47.2% female, 66.6% pathologic T1, 93.5% pathologic N0), 93 had PNI-positive tumors, among which 87.1% underwent neck dissection and 39.6% received radiotherapy. On multivariable analysis, PNI was associated with lower DFS and LRC. Adjuvant radiotherapy was not associated with improved outcomes on multivariable analysis of the entire cohort. However, among patients with PNI-positive tumors, adjuvant radiotherapy significantly decreased hazard for DFS. Conclusion: Among patients with low-risk, early-stage OCSCC, PNI was associated with worse DFS and LRC. In patients with PNI-positive tumors, adjuvant radiotherapy lowered hazard for DFS on multivariable analysis. These data support using adjuvant radiotherapy for patients with early-stage OCSCC with PNI.