Depth of Invasion as an Independent Predictor of Survival in Patients of Stage III Squamous Cell Carcinoma of the Oral Tongue

Objective Depth of invasion (DOI) has been incorporated in the new AJCC 8th classification. However, even with this new AJCC classification stage III oral tongue squamous cell carcinoma (OTSCC) remains a heterogenous group. The study aims at finding a discreet group within stage III using DOI as a cut-off of 10 mm. Methods The institutional database was reviewed from 2012 to 2018 for postoperative stage III OTSCC patients who subsequently received postoperative radiotherapy. Ninety-six patients matched the inclusion criteria. Two groups were created using a DOI cut-off of 10 mm (superficial and deep groups). The groups were analyzed for overall survival (OS) and relapse-free survival (RFS). Results The baseline and treatment characteristics were comparable between the groups except for the higher number of extensive surgeries, endophytic configuration, pT3 and, DOI in the deep group. For a median follow-up of 40.5 (range: 4-139) months, the median OS and RFS for the superficial group were not reached. The median OS and RFS for the deep group were 101 (range: 73.7-128.3) and 60 (range: 46.6-73.4) months, respectively. The difference was statistically significant for median RFS (P = .008) and trended toward significance for median OS (P = .066) for the superficial group. Multivariate Cox regression analysis showed DOI cut-off as a significant predictor for RFS but not for OS. Conclusion DOI significantly predicts poor RFS. However, showed a trend toward poor OS. This study hints toward a possibility of sub-dividing stage III OTSCC based on DOI cut-off. Level of Evidence 3 (Retrospective cohort study) Laryngoscope, 2021