Background
American Society of Clinical Oncology (ASCO) guidelines now recommend omission of sentinel lymph node biopsy (SLNB) in specific low-risk patients. However, ASCO, SOUND, and INSEMA trials note that nodal status may be needed to guide adjuvant systemic and radiotherapy treatment decisions. Importantly, some patients are uncomfortable with complete absence of axillary evaluation.
The phase 2, prospective MagUS trial used a magnetically-guided ultrasound biopsy of the SLN, showed complete concordance with SLNB (P=1.000), and enhanced accuracy of axillary ultrasound. Therefore, the MagUS technique could provide an ideal solution to de-escalate SLNB and provide nodal status for treatment decisions in low-risk patients in the setting of multidisciplinary discussion.
We present the first US data demonstrating the MagUS technique for this application in the United States.
Method
Patients eligible for omission of SLNB per ASCO guidelines, but uncomfortable with the avoidance of axillary evaluation, were consented after multidisciplinary discussion. Magtrace® (Endomag, Cambridge, UK), 1 mL, was injected sub-areolar or peritumoral 0 to 14 days prior to MagUS. A handheld magnetometer (Sentimag®, Endomag, Cambridge, UK) was used to obtain a transcutaneous Magtrace® signal and an ultrasound-imaged percutaneous core needle biopsy (Sertera 14G, Hologic, Marlborough, MA) was performed. Specimens were evaluated for brown discoloration and magnetic signal with a Sentimag® probe. If more than 1 node was identified, additional cores were taken. Biopsied nodes were clipped. Standard pathology evaluation with the addition of iron stain confirmed the presence of Magtrace within the node.
Results
Seven patients received MagUS by a fellowship-trained radiologist (Table). All patients met the ASCO SLNB omission guidelines. A fellowship-trained surgeon was present to guide the use of the Sentimag® probe for the first 2 cases. All patients (100%) had a successful transcutaneous magnetic signal to guide the core needle biopsy. Mean number of cores taken per node was 3. All patients had at least 1 core with an ex vivo probe–confirmed magnetic signal demonstrating SLN biopsy success. All pathology returned negative, and all patients avoided surgical SLNB.
Conclusion
MagUS enabled successful SLNB de-escalation of all patients and, in the context of multidisciplinary discussion, did not preclude de-escalation of radiation. Additionally, MagUS may also include improved logistical and pathway efficiencies, economic benefits, and improved patient experience. Future multi-institutional data collection will investigate these factors within the US health care system.
