Treatment Results of Postoperative Radiotherapy on Squamous Cell Carcinoma of the Oral Cavity: Coexistence of Multiple Minor Risk Factors Results in Higher Recurrence Rates

Purpose: The aim of this study was to investigate the treatment results of postoperative radiotherapy (PORT) on squamous cell carcinoma of the oral cavity (OSCC). Materials and Methods: This study included 302 OSCC patients who were treated by radical surgery and PORT. Indications for PORT include Stage III or IV OSCC according to the 2002 criteria of the American Joint Committee on Cancer, the presence of perineural invasion or lymphatic invasion, the depth of tumor invasion, or a close surgical margin. Patients with major risk factors, such as multiple nodal metastases, a positive surgical margin, or extracapsular spreading, were excluded. The prescribed dose of PORT ranged from 59.4 to 66.6Gy (median, 63Gy). Results: The 3-year overall and recurrence-free survival rates were 73% and 70%, respectively. Univariate analysis revealed that differentiation, perineural invasion, lymphatic invasion, bone invasion, location (hard palate and retromolar trigone), invasion depths ≥10mm, and margin distances ≤4mm were significant prognostic factors. The presence of multiple significant factors of univariate analysis correlated with disease recurrence. The 3-year recurrence-free survival rates were 82%, 76%, and 45% for patients with no risk factors, one or two risk factors, and three or more risk factors, respectively. After multivariate analysis, the number of risk factors and lymphatic invasion were significant prognostic factors. Conclusion: PORT may be an adequate adjuvant therapy for OSCC patients with one or two risk factors of recurrence. The presence of multiple risk factors and lymphatic invasion correlated with poor prognosis, and more aggressive treatment may need to be considered.