Comparative analysis of 99mTc-Tilmanocept (Lymphoseek) vs. 99mTc-Sulfur Colloid Sentinel Node Lymphoscintigraphy and Biopsy

Objectives Sentinel lymph node (SNL) scintigraphic mapping with intraoperative γ-probe localization is commonly used for SNL biopsy in melanoma and other malignancies. Filtered 99mTc-sulfur colloid (SC) has been the standard in the United States, but more recently 99mTc-tilmanocept (Lymphoseek) (LS) was developed as a more specific nodal targeting agent with purportedly reduced accumulation in secondary nodes. Studies have also shown faster injection site clearance with LS but similar primary sentinel node uptake when compared with SC. The objective of this study was to evaluate our own institution's experience with LS as compared to SC based on lymphoscintigraphic findings and surgical results.

Methods A retrospective chart review of patients at our institution undergoing lymphoscintigraphy with SC or LS for melanoma or other nonvulvar skin malignancy during a nine month period was performed. Breast and vulvar lymphoscintigraphy patients were excluded as the surgeons at our institution have not begun to use LS in these patients. Scintigraphic imaging reports were evaluated with respect to presence or absence of secondary nodes and lymphatic tracks. Operative notes were evaluated with respect to whether problems were encountered with node localization during surgery. A case was considered problematic if 1) counts were low resulting in the surgeon’s resorting to the alternative method of blue dye injection (which was different from his/her usual practice pattern), 2) nodes were resected but did not meet intraoperative probe criteria for SLNs, 3) a radioactive node was not encountered during surgery (failed SLNB), 4) imaging identified SNLs in more than one nodal basin but surgery did not yield a node from one of the basins.

Results During the study period 63 consecutive patients were evaluated with either SC (n=30) or LS (n=33). Melanoma accounted for the vast majority of cases (n=62) with one case of epithelioid sarcoma. These lesions originated in the head and neck (n=20), torso (n=21), or extremities (n=22). Overall lymphatic tracks were visualized in 100% of SC cases and 67% of LS cases (p=0.0004). Overall there was no statistically significant difference between secondary node observation between SC and LS (p=0.61) with 43% and 36%, respectively. Overall, problems were encountered at surgery for 6 patients, 5 of which occurred with LS, though this did not meet strict statistical significance (p=0.2). In the head and neck subgroup, 3 problematic cases were encountered, all with LS (p=0.049). Fewer potential nodes were removed per patient at surgery with SC than with LS (mean 2.1 +/- 0.8 versus 2.9 +/- 1.7, p=0.02), and although this trend continued after pathologic confirmation of the specimens it did not quite meet statistical significance (mean 2.5 +/- 1.4 versus 3.5 +/- 2.5, p=0.06).

Conclusions LS may not be superior to SC for SLN scintigraphy and SLN biopsy for melanoma. On scintigraphy the visualization of secondary nodes was similar between both groups. Tracks were quite commonly visualized with LS, although less often than with SC. In the operating room problems relating to sentinel node identification were overall infrequent for both radiotracers, however there was a small but statistically significant incidence of problems encountered with LS among head and neck cases. A statistically significant larger number of potential nodes was removed on average per patient with LS, but after pathologic confirmation the difference did not meet statistical significance.