Depth of invasion in early stage oral cavity squamous cell carcinoma: The optimal cut-off value for elective neck dissection

•Depth of invasion (DOI) is associated with lymph node metastasis in oral cancer (OC).•The AJCC (8th edition) definition of DOI in OC is recommended.•DOI ≥ 4 mm is an accurate cut-off value for elective neck dissection (END).•END performed for patients with DOI ≥ 4 mm results in lower regional recurrence. Depth of invasion (DOI) is the most important predictor for lymph node metastasis (LNM) in early stage (T1-T2) oral cancer. The aim of this study is to validate the cut-off value of 4 mm on which the decision to perform an Elective Neck Dissection (END) is made. We performed a retrospective study in patients with pathologically proven early stage oral cavity squamous cell carcinoma (OCSCC) without clinical or radiological signs of LNM, who were treated between 2013 and 2018. An END was performed when DOI was ≥ 4 mm and a watchful waiting protocol was applied in patients with DOI