Sentinel lymph node biopsy in cT1-2N0 lip squamous cell carcinoma: site-specific diagnostic accuracy, anatomic mapping, and survival impact

Optimal management of the clinically node-negative (cN0) neck in early-stage (cT1-2) lip squamous cell carcinoma (SCC) remains controversial. Sentinel lymph node biopsy (SLNB) offers a minimally invasive staging alternative to observation or elective neck dissection, but its diagnostic accuracy, lymphatic mapping patterns, and survival impact in lip SCC are not well-established. We conducted a retrospective study of 101 patients with cT1-2N0 lip SCC treated at a tertiary cancer center (2005–2022), comparing SLNB-guided management (n = 46) to observation (n = 55). Diagnostic performance of SLNB was evaluated against final histopathology. Lymphatic mapping was performed using lymphoscintigraphy/SPECT and gamma probe. Survival outcomes were analyzed using Kaplan–Meier and Cox regression, with sensitivity analysis using inverse probability of treatment weighting (IPTW). SLNB achieved a 100% detection rate and a mean yield of 3.0 sentinel lymph nodes (SLNs) per patient. Overall sensitivity was 83.3% (95% CI: 35.9–99.6%) with a false-negative rate (FNR) of 16.7%. Stratified by location, SLNB demonstrated 100% sensitivity (FNR 0%) for lower lip/midline tumors, but sensitivity decreased to 66.7% (FNR 33.3%) for upper lip tumors. Level I was the most common drainage site. Notably, facial lymph node involvement was frequently observed, particularly in lower lip SCC. SLNB was associated with significantly improved regional control compared to observation (HR 0.87, 95% CI 0.65–0.99, p = 0.046), with poorly differentiated histology also predicting worse regional control (HR 2.18, p = 0.018). However, no significant overall survival benefit was observed for SLNB (p = 0.193). IPTW analysis confirmed the regional control benefit. In cT1-2N0 lip SCC, SLNB demonstrates high diagnostic accuracy, particularly for lower lip tumors, and significantly improves regional control compared to observation, while OS benefits remain unproven. Anatomic mapping reveals distinct drainage patterns and highlights the potential importance of facial lymph nodes. These findings suggest SLNB might act as a precise staging tool to guide neck management in early-stage lip SCC.