Superparamagnetic iron oxide: a novel tracer for sentinel lymph node detection in vulvar cancer.

OBJECTIVES Superparamagnetic techniques for sentinel lymph node (SLNs) biopsy in breast cancer is well recognized but remains novel in the literature in relation to early stage vulvar cancer. The aim of this study was to compare and validate SLN detection using a superparamagnetic iron oxide tracer and a magnetometer probe compared with the standard procedure with a radioisotope (99Tc-technetium 99) and a gamma probe, in patients with vulvar cancer. METHODS Patients were included in the study with squamous vulvar tumors less than 4 cm in diameter and without suspicious groin lymph nodes on preoperative magnetic resonance imaging. Patients must have previously qualified for SLN biopsy with a radiotracer as the standard of care. The primary endpoint was the proportion of successful SLN detection with superparamagnetic iron oxide tracer versus 99Tc. The secondary endpoints were average number of SLNs retrieved per patient, proportion of SLNs detected (nodal detection rate), and proportion of pathologically positive results (malignancy rate) per patient and per node comparing both SLN detection methods. RESULTS A total of 20 patients were included in the study. SLNs were found in all patients with both methods, resulting in similar average distributions (3.1/3.2 SLN per patient). The SLN detection rate per patient was 100% with both techniques. Nodal detection sensitivity was 98.5% for the superparamagnetic technique and 93.8% for the radiotracer. Percentage of metastatic lymph nodes detected was 100% with both tracers. The rate of lymph node positivity was 21.5% (14 lymph nodes with metastases) and for patients 45% (9 patients with nodal metastases). Additionally, SLN tainted brown due to superparamagnetic iron oxide nanoparticles in 19 of 20 patients. CONCLUSIONS The use of superparamagnetic iron oxide tracer in patients with vulvar cancer seems reliable and not inferior to the standard approach with radiotracer.