Prognostic significance of anatomic site-specific depth of invasion in oral squamous cell carcinoma - An eastern Indian multi-center study

A crucial parameter in determining the prognosis of oral cavity cancer is depth of invasion (DOI). This research aimed to correlate pathological DOI at different intra-oral anatomical sites for oral squamous cell carcinoma (OSCC) with the risk of regional lymph node metastasis (LNM). This study also investigated the correlation of 3-year overall survival (OS) and disease-specific survival (DSS) with tumor depth. DOI measurement of the primary tumor at different intra-oral anatomic sites of clinically node negative patients who underwent curative surgery with elective neck dissection (END) was carried out as per AJCC 8th Edition staging guidelines in 3 DOI groups of ≤5 mm(A), >5 to ≤10 mm(B) and >10 mm(C). Association of groupwise DOI values with histopathological parameters including LNM and 3 years survival was evaluated. Univariate and multivariate logistic regression analysis (Odds ratio (OR) = 1.1 95 % CI: 1.0–1.2, p < 0.05) showed DOI to be a significant predictor for sub-clinical nodal metastasis observed in 136/382 OSCC patients. Receiver operating curve suggested that at 5 mm DOI (4 mm for early-stage OSCC), the risk of occult LNM was >20 % for all intra-oral sites combined. DOI <5 mm group demonstrated a superior 3-year OS (OR = 19.8 % CI: 7.8–49.9) and DSS (OR = 14.7 % CI: 5.9–37.0). Thus, DOI is an independent predictor of nodal metastasis and has significant association with LNM, OS and DSS. Our findings suggest that a DOI of ≥4 mm is an accurate cut-off value for performing END in early-stage OSCC and > 5 mm for advanced cases across all evaluated oral anatomic sites.