Depth of invasion as an independent prognostic factor in early-stage oral cavity squamous cell carcinoma.

PURPOSE: To determine the significance of depth of invasion as a predictor of recurrence and mortality in tongue and non-tongue early-stage oral cavity squamous cell carcinoma patients treated with surgery and no postoperative radiotherapy.

MATERIALS AND METHODS: 344 patients with oral cavity squamous cell carcinoma from 2005 to 2022 at a tertiary academic medical center were reviewed. Patients were included if they had newly diagnosed, previously untreated T1-T2N0 disease treated with surgery alone that was observed within a follow-up of 5 years. For each patient, anatomic site of oral cavity squamous cell carcinoma was categorized as either tongue or non-tongue. Cox proportional hazards regression analyses were performed to determine the association of depth of invasion with recurrence and mortality, with anatomic site, smoking status, and age at biopsy as covariates. Model assumptions were tested by statistical and graphical evaluation using Schoenfeld residuals.

RESULTS: Of 108 patients with T1-T2N0 disease, 78 (72.2 %) had tongue disease, and 30 (27.8 %) had non-tongue disease. Median follow-up was 18.2 months (range, 0.01-58.2 months). In the Cox proportional hazards models, with adjustment for anatomic site and other covariates, depth of invasion positively predicted recurrence (HR 1.16, 95 % CI: 1.01-1.32, p = 0.034) and death (HR 1.42, 95 % CI: 1.11-1.83, p = 0.006).

CONCLUSIONS: Depth of invasion is an independent predictor of recurrence and death across early-stage tongue and non-tongue squamous cell carcinoma. Therefore, depth of invasion may indicate a need for more aggressive treatment than surgery alone, such as postoperative radiotherapy, even in the absence of other adverse features on pathology within the early-stage population.