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Confirmation of Sentinel Lymph Node Identity by Analysis of Fine-Needle Biopsy Samples Using Inductively Coupled Plasma–Mass Spectrometry

¹ Department of Chemistry, Materials and Forensic Science, University of Technology, Sydney, New South Wales, Australia
² Sydney Melanoma Unit and Melanoma and Skin Cancer Research Institute, Sydney Cancer Centre, Royal Prince Alfred Hospital, Camperdown, New South Wales, Australia
³ Department of Anatomical Pathology, Royal Prince Alfred Hospital, Camperdown, New South Wales, Australia
⁴ Discipline of Pathology, The University of Sydney, Sydney, New South Wales, Australia
⁵ Discipline of Medicine, The University of Sydney, Sydney, New South Wales, Australia
⁶ Discipline of Surgery, Faculty of Medicine, The University of Sydney, Sydney, New South Wales, Australia
⁷ Department of Medical Radiation Sciences, Faculty of Health Sciences, The University of Sydney, Sydney, New South Wales, Australia
⁸ Cancer Institute New South Wales, Sydney, New South Wales, Australia
⁹ Nuclear Medicine and Diagnostic Ultrasound, RPAH Medical Centre, Newtown, New South Wales, Australia

Correspondence: Address correspondence and reprint requests to: John F. Thompson, MD FRACS FACS; E-mail: john.thompson{at}smu.org.au

Background: The sentinel lymph node (SLN) biopsy technique is a reliable means of determining the tumor-harboring status of regional lymph nodes in melanoma patients. When technetium 99 m-labeled antimony trisulfide colloid (^{99 m}Tc-Sb₂S₃) particles are used to perform preoperative lymphoscintigraphy for SLN identification, they are retained in the SLN but are absent or present in only tiny amounts in non-SLNs. The present study investigated the potential for a novel means of assessing the accuracy of surgical identification of SLNs. This involved the use of inductively coupled plasma–mass spectrometry (ICP-MS) to analyze antimony concentrations in fine-needle biopsy (FNB) samples from surgically procured lymph nodes.

Methods: A total of 47 FNB samples from surgically excised lymph nodes (32 SLNs and 15 non-SLNs) were collected. The SLNs were localized by preoperative lymphoscintigraphy that used ^{99 m}Tc-Sb₂S₃, blue dye, and gamma probe techniques. The concentrations of antimony were measured in the FNB samples by ICP-MS.

Results: The mean and median antimony concentrations (in parts per billion) were .898 and .451 in the SLNs, and .015 and .068 in the non-SLNs, the differences being highly statistically significant (P < .00005).

Conclusions: Our results show that ICP-MS analysis of antimony concentrations in FNB specimens from lymph nodes can accurately confirm the identity of SLNs. Used in conjunction with techniques such as proton magnetic resonance spectroscopy for the nonsurgical evaluation of SLNs, ICP-MS analysis of antimony concentrations in FNB samples could potentially serve as a minimally invasive alternative to surgery and histopathologic evaluation to objectively classify a given node as sentinel or nonsentinel and determine its tumor-harboring status.

Key Words: Clinical • Fine-needle biopsy • Melanoma • Pathology • Sentinel lymph node