Ultra-low dose superparamagnetic iron oxide nanoparticle injection for sentinel lymph node detection in breast cancer: prospective cohort study.

Background: Sentinel lymph node (SLN) staging is essential in breast cancer. Superparamagnetic iron oxide nanoparticles (SPIO) is a tracer where the optimal injection technique is yet not defined. The aim was to evaluate SLN detection using 0.1 ml SPIO intradermally compared to technetium-99 m (Tc99) ± blue dye.

Method: Patients planned for breast surgery and SLN biopsy received 0.1 ml SPIO intradermally at the areolar border or over the tumour. Tc99 ± blue dye was administered per clinical routine. Magnetic, radioactive, or blue nodes were removed and analysed separately. SLN detection and numbers, concordance, and skin discoloration were analysed.

Results: A total of 216 patients were included at five hospitals. Median age was 63 years, tumour size 15.9 mm, and 91.7% underwent breast conservation. SPIO was injected a median of 12 days before surgery. SLN detection was 211/216 (97.7%; 95% c.i.: 94.7 to 99.2) and 215/216 (99.5%; 95% c.i.: 98.6 to 100.0) for SPIO and Tc99 ± blue dye (P = 0.111) respectively. In total, 403 SLNs were removed; 341 detected by SPIO and 349 by Tc99 ± blue dye. The median number of SLNs was 1 (iqr: 1-2) for both tracer methods. Among 46 SLN-positive patients, 42 were correctly staged with both tracers, two with SPIO only and two with Tc99 ± blue dye only. Skin discoloration was evaluated in 107 patients. The median discoloured area was 0 cm2 (iqr: 0-0.7) among 49 patients with the injection site surgically removed and 1.3 cm2 (iqr: 0.6-2.8) among 58 without removal.

Conclusion: An ultra-low dose of 0.1 ml intradermal injection of SPIO was non-inferior to Tc99 ± blue dye for SLN detection. Skin discoloration was limited and further reduced by removal during surgery.