Risk Classification of Oral Cancer Surgical Margins: Margin to Depth of Invasion Ratio Analysis

A high-risk margin is a recurrence risk factor in oral squamous cell carcinoma (OSCC), but its exact definition is debated. The effectiveness of the margin-to-depth-of-invasion ratio (MDR) in identifying high-risk margin remains to be determined.

Patients who had a diagnosis of pT1-4N0 OSCC with negative margins (margin > 1 mm) recorded in the Taiwan Cancer Registry between January 2018 and December 2021 were reviewed. All patients were categorized into two groups: MDR < 0.5 and MDR ≥ 0.5.

The study analyzed 7420 OSCC patients without a positive margin. Of these 7420 patients, 4669 (62.92%) had an MDR ≥ 0.5, and 2751 (37.08%) had an MDR < 0.5. The group with an MDR < 0.5 exhibited significantly poorer 3-year disease-free survival (DFS, 74% vs 86%) and overall survival (OS, 79% vs 89%) than the group with an MDR ≥ 0.5. Despite a higher rate of postoperative radiotherapy (PORT) in the group with an MDR < 0.5, multivariate Cox analysis showed that patients with a margin < 5 mm and an MDR ≥ 0.5 had a significantly better DFS than those with a margin < 5 mm and an MDR < 0.5 (p = 0.001). Treatment with PORT improved DFS and OS for the patients with an MDR < 0.5, but worsened outcomes for the patients with an MDR ≥ 0.5.

For OSCC patients without positive margin, an MDR < 0.5 was associated with worse survival and higher locoregional recurrence risk. The patients with an MDR < 0.5 may benefit from PORT, whereas those with an MDR ≥ 0.5 could experience worse outcomes. An MDR < 0.5 could serve as a criterion for high-risk OSCC margin.