Indocyanine Green in Sentinel Lymph Node Biopsy for Merkel Cell Carcinoma

Key Points

  • The localization rate by node with ICG-based fluorescence was 94.8%, compared to the rate with VBD of 63.6%.
  • In two patients, a positive SLN was detected only by ICG-based fluorescence, not by gamma probe.
  • In another patient, the only positive node was identified via ICG fluorescence only.

High rates of regional lymph node involvement and metastases are not uncommon in Merkel cell carcinoma. National Comprehensive Cancer Network (NCCN) Guidelines recommend sentinel lymph node biopsy (SLNB) for staging purposes in this malignancy. In a study by Knanckstedt et al in the Journal of Surgical Research, a team researched the use of indocyanine green (ICG; a cyanine dye often used in medial diagnostics) fluorescence-based technology in SLNB detection in Merkel cell carcinoma.

Study Methods

From 2012–2017, patients with Merkel cell carcinoma who underwent SLNB with radioisotope sentinel lymph node mapping, intraoperative handheld gamma probe, and ICG-based fluorescence imaging were prospectively studied (cohort A). A group of historical controls that underwent SLNB for Merkel cell carcinoma with radioisotope sentinel lymph node mapping and vital blue dye (VBD) was also analyzed (cohort B).

Findings

Twenty-four consecutive patients underwent SLNB with sentinel lymph node mapping and ICG-based fluorescence, and 11 controls underwent SLNB with sentinel lymph node mapping and VBD.

The localization rate by node with ICG-based fluorescence was 94.8%, compared to a rate with VBD of 63.6%. In two patients, a positive SLN was detected only by ICG-based fluorescence, not by gamma probe. In another patient, the 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.

Conclusion

The researchers concluded, “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 Merkel cell carcinoma.”

The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.


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