Pterygomandibular raphe invasion as a novel grading and prognostic factor for squamous cell carcinoma of buccal mucosa: a retrospective study with propensity score matching.

Background: Squamous cell carcinoma of the buccal mucosa (SCCBM) is a prevalent malignancy of the oral cavity with high morbidity and mortality rates. The pterygomandibular raphe (PMR) connects the oral cavity, pharynx, and masticator space, serving as a key anatomical landmark during surgical resection. However, PMR invasion into SCCBM remains poorly understood. This study assessed the prognostic significance of PMR invasion in patients with resectable SCCBM.

Methods: The study included 82 patients with SCCBM, excluding those with T4b, who underwent radical resection at Kumamoto University Hospital between 2000 and 2017. Patients were categorized into three groups based on PMR invasion patterns: non-contact, contact, and invasion. The relationship between PMR invasion and clinicopathological characteristics was analyzed using the Fisher's exact test. The Kaplan-Meier method, log-rank test, and propensity score-matched analyses were used for survival analysis.

Results: Contact or invasion into the PMR was significantly associated with advanced clinical T and N stages, clinical stage, endophytic growth pattern, high-grade invasion pattern, and poor tumor differentiation. Patients with PMR invasion had a higher proportion of recurrences in the buccal subcutaneous, mandibular, and masticator spaces. Univariate analysis indicated that contact- or invasion-type PMR invasion predicted worse overall survival (OS). The impact of PMR invasion on OS was confirmed using a propensity score-matched analysis.

Conclusion: This study revealed that PMR invasion is a potential novel grading and prognostic factor for resectable SCCBM, with significance in planning the extent of SCCBM resection.