Depth Matters: Prognostic Determinants in Oral Squamous Cell Carcinoma

Background: Oral squamous cell carcinoma (OSCC) remains a major oncologic challenge, especially in South Asia. While TNM staging guides treatment, variability in outcomes underscores the need for additional prognostic markers. Depth of invasion (DOI) has recently gained recognition for its role in recurrence and survival prediction. Objective: To assess the prognostic significance of DOI in OSCC and evaluate its impact on treatment outcomes over a ten-year period. Methods: A retrospective review of 2,037 patients with OSCC treated between 2012 and 2022 was undertaken. Data on demographics, tumor site, stage, DOI, perineural invasion (PNI), worst pattern of invasion (WPOI), treatment modalities, and outcomes were analyzed. Kaplan–Meier survival analysis and chi-square tests were applied. Results: The tongue was the predominant subsite (37.5%), with a male predominance under 60 years. Advanced disease (stage III–IV) was seen in 68% of patients. Surgery with adjuvant radiotherapy/chemoradiotherapy was most frequent (40.8%). Patients with DOI <5 mm had a 3-year disease-free survival (DFS) of 92.3%, compared with 58.7% for DOI >10 mm (p < 0.001). DOI >10 mm was significantly associated with nodal spread and recurrence. PNI (31.2%) predicted regional relapse, while WPOI-5 correlated with the poorest survival outcomes. Reconstruction reduced recurrence risk but increased surgical morbidity. Quality-of-life scores were superior in patients with early-stage, low-DOI disease. Conclusion: Stratification by DOI provides superior prediction of recurrence and survival, supporting its role as a cornerstone prognostic marker in OSCC.