The updated AJCC/TNM staging system (8 th edition) for oral tongue cancer

An increasing amount of literature shows solid evidence that the depth of invasion (DOI) of oral cavity squamous cell carcinoma is an independent predictor for occult metastasis, recurrence, and survival (1-3). Furthermore, the DOI of the primary tumor has been a major criterion when deciding to perform elective neck dissection on oral cavity squamous cell carcinoma patients since as early as the mid-1990s (4). A cut-off value of 4 mm has conventionally been used when determining the need for elective neck dissection, based on a study by Kligerman et al. (4). Thereafter, several reports have proposed a range of cut-off points for improving survival, detection of occult nodal metastases, and decreasing risk of locoregional recurrence (5,6)