Sentinel lymph node biopsy (SLNB) is the primary procedure for nodal assessment in breast cancer patients. Radioisotopes (RIs) are considered the gold-standard tool. The ferromagnetic technique (superparamagnetic iron oxide-SPIO) is a non-isotope alternative SLNB method. This study compares the efficacy of SPIO and RI SLNB across two independent breast cancer centres. A total of 406 breast cancer patients, who underwent SLNB between January 2021 and December 2022, were analysed (SPIO-223 patients, RI-183 patients). Statistical tests, including Mann-Whitney U and chi-squared analyses, compared the SLN identification rates, the number of SLNs retrieved, and the positive node detection rates. The identification rates were similar for SPIO and RI (two-tailed Fisher's exact test, = 1.0). The SPIO method retrieved significantly more SLNs than RI (3.26 vs. 2.15; < 0.001). A larger proportion of patients in the SPIO group had ≥ 5 SLNs removed (20.2% vs. 8.7%; = 0.001). A statistically significant difference was observed in the proportion of metastatic SLNs to harvested SLNs between the techniques, with a larger proportion detected in the RI group (1/7.88) compared to the SPIO group (1/14.81) (chi-squared test, < 0.03). In our study, the SPIO and RI methods effectively collected SLNs. The gold-standard RI method offers distinct advantages, including its precise and consistent dosing unaffected by patient-specific factors and a highly targeted approach to node identification. These features minimise the risk of over-dissection and ensure that only the most clinically relevant nodes are removed. We note that the SPIO technique in SLNB in breast cancer patients requires further standardisation.