Background: Sentinel lymph node (SLN) biopsy is standard of care for nodal staging in patients with melanoma. SLN biopsy identifies nodal metastases in approximately 12-16% of patients with clinically node-negative melanoma. However, some literature suggests that ~5% of all tumor-positive nodal basins are incorrectly staged as sentinel node negative. In some cases, retrospective evaluation of the “negative” SLN has shown small tumor deposits that were not in the initial planes of sectioning but were identified by further sectioning of the paraffin-embedded lymph node. This suggests that intraoperative techniques to orient the SLN for histologic sectioning and pathologic analysis could increase the yield of positive SLNs and potentially decrease the rate of false- negative results. We developed a protocol for intraoperative orientation of SLN with sterile ink and studied whether intraoperative inking of the area of maximum blue dye/radioactivity (“hot spot”) within the SLN was feasible and correlated with sites of metastatic disease.
Materials and Methods: Patients with primary melanoma undergoing SLN biopsy consented to participate in this IRB-approved trial. Each SLN was evaluated intraoperatively for visual evidence of blue dye and maximum radioactive counts. The area on the SLN with the highest concentration of blue dye and/or radioactivity, if identifiable intraoperatively, was marked with ink from a sterile tissue marking kit (MarginMarker(R)). The histopathology slides were evaluated for the presence of ink and its association to metastases.
Results: 313 patients were enrolled and 309 underwent SLN biopsy. Average age was 61.3 years and most patients were male (58%). Primary melanomas had a median Breslow depth of 1.5 mm and a median of 2 mitoses/mm2 (Table 1). 290 patients had ≥1 inked SLN, while the remainder had no identifiable hot spot. 54 patients had metastatic nodal disease, of whom 40 had the positive node(s) inked for a patient-level sensitivity of 74.1% (95% CI 60.3-85.0%). At the node level, 901 SLNs were removed, of which 688 had ink identified on pathology evaluation. 75 SLNs were found to harbor metastatic disease and 62 of these had been inked and could be evaluated for correlation of the ink with the metastatic site. 48 inked SLNs harbored metastatic disease adjacent to the inked hot spot for node level sensitivity of 77.4% (95% CI 65.0-87.1).
Conclusion: Surgeon-identified orientation of SLN hot spots is feasible in a majority of cases and correlates with sites of melanoma nodal metastases. SLN inking may focus the pathologist on sections of the SLN at highest risk for metastatic involvement. Further evaluation will be required to determine if the incidence of false negative SLN biopsy results can be decreased by using intraoperative orientation techniques that allow for histopathologic analysis of nonrandom sections of the SLN.
