How Can Nanoparticles be used in Sentinel Node Detection?

Abstract

Sentinel node biopsy (SNB) is the standard of care for axillary staging in breast cancer patients with a clinically and radiologically normal axilla. The concept is based upon the exclusion of metastases in the first draining lymph node(s) from the primary tumor. The current practice utilizes a radiolabeled tracer and blue dye (combined technique) with reported sentinel node identification rates of 96.4%, and a false negative rate of 7.3% in a large meta-analysis [1]. Although successful, this technique is limited by its dependence upon radioisotopes -with their inherent strict requirements for handling, transport, disposal and close access to nuclear medicine facilities. Blue dye is also associated with prolonged skin staining and reports of anaphylaxis in 0.9% of patients [2]. These limitations have resulted in the on-going development of alternative techniques for SNB [3,4]. Magnetic technique for SNBOne of the most promising radioisotopeindependent techniques for SNB comprises an interstitial injection of superparamagnetic iron oxide (SPIO) nanoparticles, which are identified intraoperatively with a handheld magnetometer and through visual brownblack staining of nodes. The magnetic technique has now been evaluated in a number of studies and confirmed on meta-analysis to be noninferior to the radioisotope-dependent technique in breast cancer -with sentinel node identification rates of 97.1 and 96.8%, respectively [3] -and demonstrated technical benefits over other novel techniques [4]. The noninferiority of the magnetic technique has also been demonstrated in the staging of malignant melanoma [5] and has been applied to a range of solid cancers in small cohort series, which has demonstrated its feasibility in the staging of these malignancies [6][7][8]. What is still lacking is randomized controlled trial evidence, before the magnetic technique can be considered as an alternative to the standard technique. Selective axillary surgeryThe current trend within axillary management in breast cancer is toward quantification of the axillary metastatic burden. The identification of low axillary burden has been shown to allow avoidance of formal axillary node clearance, without compromising overall and disease-free survival at long-term follow-up [9]. This evidence is leading to the concept of 'selective axillary surgery', which would allow targeted excision of only metastatically involved nodes. This relies upon improved preoperative imaging combined with novel techniques to guide surgeons intraoperatively, to involved nodes. Multimodal MRI for assessing nodal involvementMagnetic nanoparticles have been used for axillary staging noninvasively with MRI and demonstrated a sensitivity and specificity for