Low Margin-To-Depth of Invasion Ratio Plus pN1 Predict Poor Prognosis in Oral Cancer Without Adverse Features

Objective: To evaluate the prognostic value of the margin-to–depth of invasion ratio (MDR) combined with nodal classification in stages I–III oral squamous cell carcinoma (OSCC) without conventional adverse pathological features (CAPFs) treated with curative resection alone. Methods: This retrospective study included 820 patients with pT1–3N0–1 OSCC without CAPFs treated with curative resection without adjuvant therapy between January 2005 and April 2017 at a tertiary referral center. The MDR cutoff was identified using Youden's index with bootstrap validation. Cancer-specific survival (CSS) and relapse-free survival (RFS) were analyzed using Cox models. Results: An MDR cutoff of 0.92 stratified outcomes. MDR ≥ 0.92 was associated with better 5-year CSS (96.8% vs. 90.0%; p < 0.001) and RFS (88.6% vs. 81.5%). Low MDR and pN1 were independent adverse predictors. The combined cohort identified a small but highly aggressive subgroup: patients with low MDR plus pN1 (n = 16) had the worst outcomes (5-year CSS 56.3%, 95% CI: 36.5%–86.7%; 5-year RFS 37.5%, 95% CI: 19.9%–70.6%) compared with the other subgroups. Conclusion: Low MDR plus pN1 identified a high-risk subgroup in OSCC without CAPFs; accordingly, patients with both features might require closer surveillance and further evaluation of adjuvant treatment strategies in clinical situations.