Single-Tracer Methylene Blue-Guided Sentinel Lymph Node Biopsy in Early-Stage Squamous Cell Carcinoma of the Buccal Mucosa: A Prospective Study.

Background: Subsite and tumor stage-related heterogeneity in studies on optical tracer-guided sentinel lymph node biopsy (SLNB) in oral squamous cell carcinoma (SCC) has led to inconsistent results, limiting the applicability and wider adoption of this technique.

Methodology: This single-center, prospective validation study conducted in January and February 2022, included 29 consecutive patients with early-stage, node-negative SCC of the buccal mucosa undergoing methylene blue-guided SLNB followed by modified radical neck dissection (considered the reference standard) to determine the identification rate and test validity of SLNB, and secondarily, the clinicopathological factors associated with node-positivity using binary logistic regression.

Results: SLN identification rate with methylene blue was 93.1% with 66 SLNs retrieved in 27 patients, at a median 2 (IQR 2-3) nodes per procedure. Additionally, 644 nodes were grossed in the neck dissection specimens of 29 patients (median yield 24; IQR 17.5-26 per procedure). Overall accuracy of SLNB was 96.3% (95%CI 81.03-99.91%), with sensitivity and negative predictive value of 83.3% (95%CI 35.88-99.58%) and 95.5% (95%CI 77.16-99.88%), respectively. The only factor independently predictive of occult nodal involvement was pathological depth of infiltration (hazard ratio 3.312; 95%CI 1.040-10.546, p = 0.043) which at 6.5 mm was 100% sensitive and 91.3% specific (area under curve 0.975; 95%CI 0.925-1.000).

Conclusion: Methylene blue-guided SLNB may be considered a viable alternative to evaluate the neck in early-stage buccal mucosal SCC with acceptable test validity and reliability. [Registered with the Clinical Trials Registry of India (CTRI/2022/01/039523 dated 18th January 2022)].