A Novel Method for Intraoperative Sentinel Lymph Node Detection in Prostate Cancer Patients Using Superparamagnetic Iron Oxide Nanoparticles and a Handheld Magnetometer: The Initial Clinical Experience

BACKGROUND: A sentinel lymph node (SLN) biopsy using superparamagnetic iron oxide nanoparticles (SPIOs) as a tracer instead of radioisotopes was first applied successfully in breast cancer. This study determined the feasibility of this new technique using SPIOs and a handheld magnetometer to detect SLNs in prostate cancer (PC). METHODS: Enrolled 20 patients with intermediate and high-risk PC (PSA >10 and/or Gleason score >7) in a prospective study (12/2013–1/2014; DRKS00005473), following an ethics committee approval. After transrectal intraprostatic SPIOs injection a day earlier, patients (19/20) underwent magnetometer-guided sentinel lymphadenectomy (sPLND) and extended PLND, followed by radical prostatectomy. One patient was not operated because of an unrelated coagulation disorder. The ex vivo magnetic activity of all lymph nodes (LNs) removed was measured. The detection rate, rate of in vivo detected SLNs, and sensitivity of sPLND was established. RESULTS: No adverse events attributable to SPIOs injection were observed. Identified 126 SLNs (median 7, IQR 4–9) and resected 334 LNs (median 17, IQR 14–19); 37 % (7/19) of the patients had LN metastases (median 1, IQR 1–3.5). The detection rate and rate of in vivo detected SLNs were 90 % (17/19) and 94 % (118/126) respectively. Using sPLND, all LN metastases were detected (15/15, sensitivity 100 %) in all patients identified with SLNs. One LN + patient showed no SLNs following transurethral prostate resection. CONCLUSIONS: This is the first study using a magnetic tracer and magnetometer to detect SLNs in PC. Initial data indicate that this simple, radiation-free procedure is safe, feasible, and reliably identifies SLN and LN metastases in most patients.