Magnetically guided surgery after primary systemic therapy for breast cancer: implications for enhanced axillary mapping.

Background: Superparamagnetic iron nanoparticles perform comparably to radioisotope ± blue dye for sentinel lymph node detection in breast cancer, even when injected up to 8 weeks before surgery. Using superparamagnetic iron nanoparticles for sentinel lymph node detection after primary systemic therapy, and the maximum time frame of superparamagnetic iron nanoparticle administration have not been investigated.

Methods: This cohort study included cN0/1-to-ycN0 patients undergoing sentinel lymph node detection or targeted axillary dissection. All patients received superparamagnetic iron nanoparticles either before primary systemic therapy or before surgery, and radioisotope on the day of surgery.

Results: For 113 patients analysed, superparamagnetic iron nanoparticles were injected a median of 3 (range 0-248) days before surgery, with a 97.4% detection rate compared with 91.2% for radioisotope (P = 0.057). Concordance for radioisotope was 97.1% and this was not affected by timing of superparamagnetic iron nanoparticle injection (Kendall's tau 0.027; P = 0.746). The median sentinel lymph node yield was 3 (interquartile range (i.q.r.) 2-3) for superparamagnetic iron nanoparticles and 2 (i.q.r. 2-3) for radioisotope (P < 0.001). In targeted axillary dissection, detection was 100% for superparamagnetic iron nanoparticles and 81.8% for radioisotope (P = 0.124). The index node was magnetic in 93.9% and radioactive in 66.7% (P = 0.007), an outcome that was not affected by any factors. For patients with metastases, superparamagnetic iron nanoparticle detection was 100% and radioisotope-based detection was 84.2% (P = 0.083), with superparamagnetic iron nanoparticles detecting more metastatic sentinel lymph nodes (median of 1 (i.q.r. 1-2) for superparamagnetic iron nanoparticles compared with a median of 1 (i.q.r. 0-1) for radioisotope; P = 0.005).

Conclusion: Injection before primary systemic therapy is feasible and does not affect concordance with radioisotope. Superparamagnetic iron nanoparticles perform comparably to radioisotope, but detect more sentinel lymph nodes and have a higher rate of detection of metastatic sentinel lymph nodes.