Image-Guided Pre-Operative Magnetic Seed Localization of Breast Lesions: Experience of a Northern Ontario Hospital with the Magnetic Occult Lesion Localization Instrument (MOLLI): MOLLI seed localization

Background: Breast cancer remains one of the leading malignancies among Canadian women. Lumpectomies have been increasing in number over total mastectomies due to comparable survival and lower reoperation rates. While wire localization has been the traditional method for the localization of non-palpable breast lesions, it presents logistical and patient comfort challenges. Magnetic localization systems, such as the Magnetic Occult Lesion Localization Instrument (MOLLI), offer an alternative with potential advantages. Methods: A retrospective review was conducted, examining the outcomes of 145 patients who underwent MOLLI seed localization between December 2023 and October 2024. A total of 154 seeds were placed, with localization performed predominantly via sonographic guidance. The primary outcomes were placement success, retrieval rates, margin status of the surgical specimens, and the number of days between seed placement and surgical excision. Results: The mean patient age was 62 years. MOLLI seeds were successfully placed in 100% of cases, with 76% within or adjacent to the lesion. Of the excised lesions, 70.3% were malignant, with a positive margin rate of 17.3%, which was defined as invasive carcinoma or ductal carcinoma in situ (DCIS) being less than 2 mm from the margins. The MOLLI seeds were successfully retrieved in 100% of cases. Conclusion: The MOLLI localization system demonstrated high accuracy and retrieval success, offering a viable alternative to traditional wire localization. The findings suggest MOLLI and other magnetic localizers may improve lesion localization and excision while also improving patient comfort. As this was a retrospective single-center study, further large-scale trials are needed to confirm generalizability.