Detection and distribution of superparamagnetic nanoparticles in lymphatic tissue in a breast cancer model for magnetic particle imaging

Introduction The axillary lymph node extraction (ALNE) is part of the surgical staging in breast cancer. Radical ALNE was associated with high morbidity and significant loss of QoL. The adverse effects decreased since the introduction of the sentinel lymph node biopsy (SNLB), with dyes and radio nuclides as tracer substances. They could be replaced by super paramagnetic iron oxide nano particles (SPIOs). Through the magnetic particle imaging (MPI), a 3D-imaging and distinct localization of SPIOs can be achieved in SNLB. Qualitative and quantitative enrichment of SPIOs in the axillary lymphatic tissue is unexplored until now. Methods We aim to prove the principle of SNLB by MPI within a healthy mouse model and than in a tumor bearing mouse model with metastatic axillary lymph nodes. Axillary and environmental tissues are analyzed with different techniques: histology, Prussian blue staining, electron microscopy, atomic absorption spectrometry and MPI spectrometry. Results The SPIOs are moving from the injection site through the lymph-fat tissue to the axillary region and finally into the axillary lymph nodes. They are following the traces of lymphatic vessels, respecting the borders and spaces between different tissues e.g. muscle fibers. SPIOs were found in the neighborhood of collagen fibers. They accumulate in the cortex region of lymph nodes. We present first results of the approach of SNLB by MPI. Conclusion The use of SPIOs and the MPI technique as SNLB tracer and finder as a new SNLB technique will be less complex and incriminating for patient and staff and makes it more precise. A MPI hand probe for use in the operating theatre is under construction. Therewith the SNL detection can be easily performed and by the avoidance of intensive surgical exploration the morbidity is dramatically reduced. The tracer for MPI is easy to obtain. This makes the method accessible to all patients. The concept of SNLB by MPI can be applied in principle in all solid tumors.