Elective Neck Dissection Strategies Guided by AJCC-8 Depth-of-Invasion (DOI) in cT1–T2N0 Oral Cavity Cancer—A Systematic Review

BACKGROUND/OBJECTIVES: Clinically node-negative (cN0) neck management in cT1-T2 oral cavity squamous cell carcinoma continues to be a subject of controversy. The eighth edition AJCC has incorporated depth of invasion (DOI) as a significant factor in staging and consideration for possible neck dissection. Establishment of accurate DOI thresholds and their clinical relevance is crucial to maximize oncological outcomes with reduced unnecessary morbidity. METHODS: A comprehensive analysis of clinical research assessing elective neck dissection (END) techniques in oral cavity cancers classified by DOI in cT1-T2N0 patients was carried out. The included studies reported occult nodal metastasis rates, overall survival, disease-specific survival, disease-free survival, and regional control. RESULTS: With hazard ratios favoring END for overall survival (HR 0.64; 95% CI 0.45-0.92) and disease-free survival (HR 0.45; 95% CI 0.34-0.59), elective neck dissection provided advantages in both survival and regional control. In a national registry, DOI ≥ 5 mm independently raised the risk of nodal failure (HR 2.099; 95% CI 1.346-3.271), while END enhanced neck control in comparison to observation (HR 1.749; 95% CI 1.141-2.680). With ROC-derived cut-offs like 4.59 mm producing positive predictive values for nodal metastasis up to 41.7%, diagnostic thresholds clustered around 4 mm. CONCLUSIONS: Under DOI guidance, elective neck dissection consistently showed oncologic benefit, with practical thresholds convergent around 4 mm for sites in the mixed oral cavity and 3 mm for high-risk subsites. The synthesized results confirmed that DOI is the primary determinant of END when combined with histopathologic and subsite-specific risk factors.