Antimony concentrations in nodal tissue can confirm sentinel node identity.

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 (50 microm) 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.

Failure to remove true sentinel nodes can cause failure of the sentinel node biopsy technique: evidence from antimony concentrations in false-negative sentinel nodes from melanoma patients.

We have recently found that antimony (originating from the technetium 99m antimony trisulfide colloid, used for preoperative lymphoscintigraphy) can be measured in tissue sections from archival paraffin blocks of sentinel nodes (SNs) by means of inductively coupled plasma mass spectrometry (ICP-MS) to confirm that removed nodes are true SNs. We performed a retrospective analysis of antimony concentrations in all our false-negative (FN) SNs to determine whether errors in lymphadenectomy (i.e., failure to remove true SNs) may be a cause of FN SN biopsies (SNBs). Among 27 patients with an FN SNB, metastases were found on histopathologic review of the original slides or additional sections in 7 of 23 patients for which they were available; however, antimony concentrations were low in 5 of 20 presumptive SNs. Our results suggest that an FN SNB can occur because of failure to remove the true SN as well as histopathologic misdiagnosis.