Koichi Koizumi

Background: Postoperative adjuvant therapy strategies are generally determined based on pathological risk stratification in oral cancer. However, the efficacy of postoperative adjuvant therapy in patients with intermediate‐risk factors for recurrence of oral cancer such as close surgical margins, pT3–T4 classification, pN2–N3 nodal status, perineural invasion, vascular invasion, lymphatic invasion and pattern of invasion remains unclear, and no standardized treatment guidelines or consensus have been established to date. Therefore, this study retrospectively analyzed the clinical significance of risk factors for pathological recurrence in patients with advanced oral cancer and evaluated the impact of postoperative adjuvant therapy on patient prognosis. Methods: This retrospective clinical study included 130 patients who underwent initial radical surgical resection for advanced oral squamous cell carcinoma (OSCC) at our institution between January 2010 and December 2023. The postoperative recurrence risk factors included ENE of the cervical lymph nodes, positive surgical margins, close surgical margins, pathological T classification (pT3 or pT4), pathological N classification (pN2 or pN3), metastasis to level IV or V lymph nodes, perineural invasion, vascular invasion, and lymphatic invasion. We analyzed the relationships among the presence of these risk factors, administration of postoperative adjuvant therapy (RT or CRT), occurrence of recurrence or metastasis, and patient prognosis (DFS). Results: Patients with lymphatic invasion had a significantly lower survival rate than those without lymphatic invasion (66.7% vs. 82.8%, p < 0.05). Although pT4, pN2–N3, perineural invasion‐positive and vascular invasion‐positive did not reach statistical significance, a trend toward reduced survival was observed in each case. The perineural invasion‐positive group had significantly higher recurrence and metastasis rates than the perineural invasion‐negative group (51.9% vs. 23.6%, p < 0.05). Multivariate analysis using logistic regression also confirmed the presence of perineural invasion as an independent prognostic factor (HR = 4.496, p = 0.019). Conclusions: This study demonstrated that perineural invasion is a significant risk factor for recurrence and that lymphatic invasion is a poor prognostic factor in oral cancer. Postoperative adjuvant therapy in patients with perineural or lymphatic invasion‐positive disease contributed to reduced recurrence rates and prolonged survival. These findings suggest that the pathological evaluation of perineural and lymphatic invasions is an important indicator in determining the appropriateness of postoperative adjuvant therapy.