Sentinel Lymph Node Biopsy for Early-Stage Oral Cavity Cancer: Analysis of Diagnostic Accuracy and False-Negative Cases

Background/Objectives: Identifying the causes of sentinel lymph node biopsy (SLNB) failure in early-stage oral cavity squamous cell carcinoma (OCSCC) is essential for refining surgical protocols and optimizing patient selection. This study aimed to evaluate the diagnostic performance, predictors of false-negative (FN) results, and long-term oncological outcomes of SLNB in patients with early-stage OCSCC. Methods: A retrospective, single-centre cohort study was conducted on 220 patients with cT1–cT2 N0 M0 OCSCC who were surgically treated between 2017 and 2024. Preoperative lymphatic mapping was performed using 99mTc-nanocolloid and SPECT/CT. All sentinel lymph nodes (SLNs) underwent an ultrastaging protocol involving serial sectioning and immunohistochemistry. Diagnostic accuracy, survival outcomes, and clinicopathological predictors of FNs were analysed. Results: The SLN identification rate was 99.1%. Metastatic involvement was detected in 49 patients (22.3%), preventing 77.7% of the cohort from undergoing unnecessary neck dissection. Bilateral lymphatic drainage was observed in 55.9% of floor of the mouth tumours. During a median follow-up of 36 months, the diagnostic performance showed a sensitivity of 81.7%, a negative predictive value of 93.6%, and an overall accuracy of 95.0%. Analysis of the 11 FN cases showed that both depth of invasion (DOI) (6.0 mm vs. 3.0 mm; p = 0.010) and maximal tumour dimension (25 mm vs. 15 mm; p = 0.0008) were significant predictors of diagnostic failure. The five-year overall survival rate was significantly superior in patients with negative SLNs compared to the SLN-positive group (82% vs. 61%; p < 0.001). Conclusions: SLNB is an accurate and reliable staging tool for early-stage OCSCC, providing personalised lymphatic mapping that harmonizes oncological efficacy with the avoidance of overtreatment. However, an increased DOI and a larger tumour size significantly raise the risk of FN events, indicating the need for close postoperative surveillance in these high-risk subgroups.