Utilization of Indocyanine Green to Aid in Identifying Sentinel Lymph Nodes in Merkel Cell Cancer.

BACKGROUND: Merkel cell carcinoma (MCC) is a relatively rare skin cancer with high rates of regional lymph node involvement and metastatic spread. National Comprehensive Cancer Network guidelines recommend sentinel lymph node biopsy (SLNB) for staging purposes. The goal of this study is to report our experience utilizing indocyanine green (ICG) fluorescence-based technology to aid in SLNB detection in MCC.

METHODS: Consecutive MCC patients who underwent SLNB with radioisotope lymphoscintigraphy, with intraoperative handheld gamma probe, and ICG-based fluorescence imaging from 2012 to 2017 were prospectively studied (Cohort A). A group of historical controls that underwent SLNB for MCC with radioisotope lymphoscintigraphy and vital blue dye (VBD) (lymphazurin or methylene blue dye) was also analyzed (Cohort B).

RESULTS: Twenty-four consecutive patients underwent SLNB with lymphoscintigraphy and ICG-based fluorescence and 11 controls underwent SLNB with lymphoscintigraphy and VBD. The localization rate by node with VBD was 63.6% and ICG-based fluorescence was 94.8%. For two patients, a positive sentinel lymph node (SLN) was detected only by ICG-based fluorescence and the nodes were not detected by gamma probe and one patient's only positive node was identified via ICG fluorescence only. VBD or gamma probe did not identify any unique positive SLNs in either cohort B or either cohort, respectively.

CONCLUSIONS: In this study, we indicate that ICG-based fluorescence is not only feasible to augment SLN identification, but it has a higher node localization rate as compared to blue dye and it was able to identify positive SLNs otherwise missed by gamma probe. This study suggests the importance of utilizing two modalities to augment SLN identification and that ICG-based fluorescence may be able to identify nodes that would have been otherwise missed by gamma probe. We will continue to follow these patients and enroll more patients in this prospective study to further determine the role that ICG-based fluorescence has in identifying sentinel lymph nodes in MCC.