Superparamagnetic iron oxide nanoparticles as the sole method for sentinel node biopsy detection in patients with breast cancer

Background: Sentinel node biopsy (SNB) using superparamagnetic iron oxide (SPIO) nanoparticles is a novel method in breast cancer. Several studies have verified the non-inferiority of SPIO compared with the standard use of radioisotope Tc-99m with or without blue dye. The aim of the MONOS study presented here was to evaluate the use of SPIO as a sole tracer and the efficacy of tracer injection in the preoperative setting. Methods: This prospective cohort study was carried out in two hospitals, one using Tc-99m and the other SPIO. Tc-99m was injected in the morning of the day of surgery or the day before. SPIO was either injected before surgery in the outpatient clinic or 1 h before the operation. Results: A total of 338 consecutive patients with breast cancer underwent 343 procedures; SPIO nanoparticles were used in 184 procedures and Tc-99m-labelled tracer in 159. Detection rates for SPIO and Tc-99m were 95.6 and 96.9 per cent respectively (P = 0.537). All nodes with SPIO uptake were coloured brown. Fewer nodes were retrieved with SPIO (mean 1.35 versus 1.89), regardless of whether blue dye was used (P < 0.001). Preoperative SPIO injection (58.7 per cent of procedures), a median of 16 (range 2-27) days before the procedure, was associated with a better tracer-specific detection rate (95.3 versus 86 per cent; P = 0.031) and retrieval of more nodes (mean 1.43 versus 1.03; P < 0.001) than perioperative administration. Skin staining was present in 39.9 per cent of patients, and was related to breast-conserving surgery and periareolar injection. Conclusion: The use of SPIO alone is a safe alternative, with results comparable to those of the standard dual technique using Tc-99m and blue dye. The efficacy of injection in the preoperative setting simplifies logistics and improves performance. Skin staining can be prevented by a deeper peritumoral injection.