Superparamagnetic iron oxide as a tracer for sentinel node biopsy in breast cancer: A comparative non-inferiority study.

Aims: The gold standard for detection of Sentinel Lymph Nodes (SLN) is a combined radioisotope and blue dye breast injection, using a gamma probe (GP). A new, non-radioactive method was developed, using a tracer (Sienna+(®)) of superparamagnetic iron oxide (SPIO) nanoparticles and a manual magnetometer (SentiMag(®)) (SM). The IMAGINE study was designed to show the non-inferiority of SM compared to GP, for the detection of SLN in breast cancer patients with SLN biopsy indication.

Methods: From November 2013 to June 2014, 181 patients were recruited, and 321 nodes were excised and assessed ex-vivo. Readings from both SM and GP devices were recorded during transcutaneous, intraoperative, and ex-vivo detection attempts.

Results: At the patient level, ex-vivo detection rates (primary variable) with SM and GP were 97.8% and 98.3% (concordance rate 99.4%). Transcutaneous and intraoperative detection rates were 95.5% vs 97.2%, and 97.2% vs 97.8% for SM and GP respectively (concordance rates > 97%). At the node level, intraoperative and ex-vivo detection rates were 92.5% vs 89.3% and 91.0% vs 86.3% for SM and GP respectively. In all cases the non-inferiority of SM compared to SM was shown by ruling out a predefined non-inferiority margin of 5%.

Conclusions: Our study showed the non-inferiority of SM as compared to GP. Moreover, the ex-vivo and intraoperative detection rates at the node level were slightly higher with SM.