(LSM P2) 40 Minutes is Enough: Lymphoscintigraphy with Novel Agent Reduces Time Needed for Mapping

Introduction: Preoperative lymphoscintigraphy is essential to localize sentinel lymph nodes (SLN) in melanoma. In 2014, technetium Tc 99m tilmanocept (tilmanocept) replaced technetium Tc 99m-sulfur colloid (Tc-99m SC) as the preferred lymphoscintigraphy agent at two institutions. This study compares the effectiveness of the two mapping agents in terms of mapping times, intra-operative identification of SLN, and false negative (FN) rate.

Methods: Patients with truncal, head, or neck melanoma who underwent sentinel lymph node biopsy (SLNB) between 2010-2018 were identified at the two study institutions. Retrospective patient demographic, tumor, and imaging data was stratified by receipt of Tc-99m SC (n=257) or tilmanocept (n=134). Student’s t-test and Mann-Whitney U test were used to compare the number of SLN identified, mapping times, and FN rate.

Results: The tilmanocept and Tc-99m SC groups were similar in demographic and primary tumor characteristics. Tilmanocept and Tc-99m SC identified a similar total number of SLN (3.09 vs 3.25, p = 0.408). However, tilmanocept required shorter lymphoscintigraphy mapping times (37.9 vs 85.6 minutes, p <0.01). Within the first ten minutes of mapping, tilmanocept identified 59.7% of total SLN compared to Tc-99m SC identifying 29.1% (p<0.01). There was no significant difference in the number of patients with positive SLN (tilmanocept 17.9 vs Tc-99m SC 11.1%, p=0.083). The FN rate at median follow up time 23.2 months was similar, 33% for tilmanocept and 32% for Tc-99m SC.

Conclusion: In comparison to Tc-99m SC, tilmanocept requires significant less lymphoscintigraphy mapping time while identifying similar number of SLN and maintaining similar FN rates.