Effectiveness of sentinel lymph node scintigraphy and intraoperative gamma probing with gold standard elective neck dissection in patients with N0 oral squamous cell cancers
Authors: Sundaram Palaniswamy Shanmuga , Subramanyam Padma 
Published: September 2019

Objective
Oral cancer ranks in the top three of all cancers in India, accounting for over 30% of all cancers reported. Elective neck dissection (END) is the mainstay of treatment in early disease. Performing ENDs for node negative (N0) patients can result in significant morbidity with questionable benefit and impair the patients’ quality of life. Sentinel Lymph Node Biopsy (SLNB), is an emerging investigation helping in risk stratification of patients with early oral cancer and node negative disease. SLNB is a simple, easy to perform investigation with a high sensitivity and plays a major role in avoiding neck dissection. Studies have compared SLNB-based neck dissection with END in early oral cancers, and also on survival benefit with prophylactic neck dissection at the time of primary surgery as compared to watchful waiting followed by therapeutic neck dissection for nodal relapse, in patients with clinical N0 (cN0) oral squamous cell carcinoma (OSCC) on literature search.

Aim
Our primary aim was to determine the effectiveness of lymphoscintigraphy in OSCC in clinically neck node negative (cN0) patients in comparison to gold standard END for nodal metastases identification and secondly to assess the utility of gamma probe in guiding SLNB in this group of patients.

Materials and Methods
Fifty-eight patients (M:F = 42:16) with histologically confirmed OSCC of T1-3 stage with cN0 and planned for curative intent primary surgical treatment were divided into two arms. All patients underwent sentinel lymph node (SLN) imaging and biopsy. Arm 1 underwent nodal dissection based on SLNB positivity, while all patients in arm 2 had wide neck dissection irrespective of SLNB findings.

Results
SLN was detected in all 58 patients, 96.4% patients showed SLN immediately postinjection. More than one SLN was found in 94.3% patients and 6.8% patients showed contralateral SLN also. Higher proportion of nodal metastasis were observed in tongue cancers than in remaining floor of mouth and buccal mucosa cancers (38% vs 12%, P< 0.01). We also found significant association between T size and nodal metastasis in our series. Sensitivity of SLNB was 88.23% with a specificity of 100%, both for SLN imaging and gamma probing localization reflecting the reliability of this technique. Serial step sectioning at 150 micrometre is recommended. SLNB showed positive nodes in 29.3 % patients with cN0 neck. We found that the association between the outcome in both arms was not statistically significant. On follow-up, three patients with T3N0 OSCC of arm 2 had nodal recurrence/lung metastases. One patient of arm 1 had nodal recurrence. Two patients expired within one year. As high as 73% patients (22 negative necks out of 30) had unwarranted neck dissection in arm 2.

Conclusion
SLNB is an effective method to circumvent unwarranted neck dissection in early OSCC and prevent complications. Gamma probing is a robust and easy tool to identify SLN in T1-3 stages with N0 necks clinically. A positive SLNB is found to be reliable in guiding neck dissection in this small study. Larger studies are warranted to establish its recommendation in routine clinical practice.