Abstract PO5-23-01: SentiNeo: A feasibility study on a magnetic approach to targeted axillary dissection and sentinel lymph node biopsy after neoadjuvant chemotherapy

Abstract Background Neoadjuvant chemotherapy (NAC) is increasingly used to treat certain breast cancer subtypes, and often, with good axillary response. Axillary management after NAC has become a contentious topic. Low detection rates and high false negative rates for sentinel lymph node biopsies (SLNB) could be due to the chemotherapy-induced fibrosis and blockage of the lymphatic drainage. Complete axillary response raises the dilemma of whether axillary clearance is still necessary after NAC in node positive patients. Targeted axillary dissection (TAD) is a safe alternative but the optimal method for index metastatic lymph node marking and lymphatic mapping of additional SLNs is largely undetermined. In SentiNeo, we study the feasibility and accuracy of using superparamagnetic iron oxides nanoparticles (SPIO) and magnetic seeds for axillary staging after NAC. Methods: Patients from two hospitals undergoing NAC were included: 40 without (cN0) and 40 with (cN+) axillary metastases. For cN0, SPIO was injected before and Technetium (Tc99) after NAC. For cN+, a magnetic clip was inserted into the index metastatic node together with SPIO injection before and Tc99 after NAC. Endpoints were 1) Index node detection and 2) SLN detection and concordance rates. Detection rate was defined as the proportion of patients who had SLNs detected as per tracer (using both magnetometer and gamma probe). Concordance was defined as the number of nodes marked by both SPIO and Tc99, divided by the total number of Tc99 marked nodes. As this is a feasibility study, no calculations for statistical significance were done. Results: All 80 patients have been included and 60 have completed NAC and surgery: 35 cN0 with SLNB and 25 cN+ with TAD. Overall, SLN detection rates (excluding the index nodes) were 83.3% (50/60) for SPIO and 76.7% (46/60) for Tc99. In cN0, SLN detection rate was 85.7% (30/35) for SPIO) and 88.6% (31/35) for Tc99. In cN+, the index node was found in 24 of 25 patients. One patient did not receive a magnetic clip due to administrative error. The SLN detection rate (excluding index nodes) was 80% (20/25) for SPIO) and 60% (15/25) for Tc99. In total, 142 lymph nodes were retrieved, of which 71 contained both tracers. The concordance was 84% (out of 84 nodes detected with Tc99, 71 were also detected with SPIO). However, the reversed concordance was only 55% (out of 129 nodes detected with SPIO, 71 were radioactive). The overall mean (median) number of retrieved nodes were 2.2 (2) for SPIO and 1.4 (1) for Tc99. Conclusions: In this pilot study we have shown that injecting SPIO before NAC is feasible with detection rates comparable to Tc99injected after NAC. More nodes were retrieved with SPIO and furthermore, we hypothesize that these nodes might be more representative than nodes detected with a tracer injected after NAC. Finding the index node using the SentiMag probe was easy. For SLN detection with SPIO the same probe was used, making the magnetic approach to axillary staging an appealing alternative with no need for an extra localisation before surgery or access to nuclear medicine facilities. These findings justify a larger study which is in planning. Table. Citation Format: Kian Chin, Roger Olofsson Bagge, Nushin Mirzaei, Anikó Kovács, Henrik Leonhardt, Pontus Zaar, Andreas Karakatsanis, Eirini Pantiora, Staffan Eriksson, Maria Ekholm, Alastair Thompson, Peter Barry, Michael Boland, Vivian Man, Ava Kwong, Fredrik Wärnberg. SentiNeo: A feasibility study on a magnetic approach to targeted axillary dissection and sentinel lymph node biopsy after neoadjuvant chemotherapy [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-23-01.