Magnetic Sentinel Lymph Node Biopsy in Early Breast Cancer Patients: An Individual Patient Data Meta-analysis of Tracer Uptake

Background: Superparamagnetic iron oxide nanoparticles (SPIO) are emerging as a viable alternative to technetium and blue dye. Our study was designed to evaluate the correlation between SPIO dose, injection site, and timing with sentinel lymph node (SLN) detection and iron content in retrieved SLNs.

Methods: This study combined individual patient data from three Dutch and five Swedish studies. Associations between SLN detection and dose, site, and timeframe of SPIO injection were examined. The iron content for each retrieved SLNs with or without metastases were calculated according to a predefined look up table based on probe counts and sensitivity setting. Analyses were conducted by using multivariable logistic and linear regression models using generalized estimating equation.

Results: A total of 908 patients were included. The detection between the magnetic technique (96.6%) and the radioactive technique was comparable (96.6% vs. 96.8%, p = 0.75). The 1.0-mL SPIO dose was associated with the highest, and <0.5 mL of SPIO was associated with the lowest patient-based detection (100.0 and 96.6% respectively). An intratumoural injection was found to be less favourable compared with peritumoural and subareolar, whereas injection >168 hours before surgery demonstrated the highest patient-based detection.

Conclusions: The noninferiority of SPIO compared with technetium99m ± BD has been proven by several studies. A dose of 1 mL, around the areola, with a longer exposure time, appears to increase the SPIO uptake in the nodes and SLN detection. Metastatic burden in SLNs did not significantly impact the uptake of SPIO.