Abstract:
The sentinel node biopsy procedure is a highly accurate method of staging patients with cutaneous melanoma
and the tumor-harboring status of sentinel nodes is the most important prognostic factor. For the procedure to
provide accurate prognostic information, however, it is essential that 'true' sentinel nodes are removed and
examined thoroughly. A technique to confirm sentinel node Identity may reduce the false-negative rate of the
procedure. We have found that antimony (originating from the antimony sulfide colloid used for preoperative
lymphoscintigraphy in our institution) can be measured in tissue sections of sentinel nodes using Inductively
coupled plasma mass spectrometry. The aims of this study were to determine whether antimony concentrations
can be used to confirm that removed sentinel nodes are 'true' sentinel nodes and to differentiate sentinel nodes
from nonsentinel nodes. In all, 24 patients who had both a tumor-positive sentinel node and a tumor-negative
nonsentinel node removed from one regional node field during the same operation, were identified. Tissue
sections (50pm) thick were cut from archival paraffin blocks of each of the sentinel nodes and nonsentinel
nodes. Antimony concentrations in the tissue sections were measured using inductively coupled plasma mass
spectrometry. The median and mean concentrations of antimony in parts per billion were 0.526 and 1.198,
respectively (range 0.020-7.596) in the sentinel nodes, and 0.043 and 0.123 (range 0-0.800) in the nonsentinel
nodes (p= 0.004). In four of the 24 pairs, both the presumed sentinel nodes and the nonsentinel nodes had very
low antimony levels (less than 0.18 parts per billion), suggesting that nodes designated as sentinel nodes may
not have been 'true' sentinel nodes. It Is concluded that determination of antimony concentrations within
sentinel nodes using the highly sensitive method of inductively coupled plasma mass spectrometry can
confirm the Identity of sentinel nodes and validate the sentinel node technique.
