Effectiveness and Safety of Magseed Localization for Excision of Breast Lesions: A Prospective, Phase IV Trial

OBJECTIVE: A prospective, phase IV study was conducted to assess the effectiveness of Magseed to localize breast lesions requiring surgical excision. BACKGROUND: Since Food and Drug Administration approval in 2016, Magseed has been increasingly used to localize nonpalpable lesions due to advantages over wires or radioactive seeds. This is the first prospective, postmarketing trial of Magseed. METHODS: From January 2017 to February 2018, 107 women with lesions requiring localization were enrolled at a single institution. Primary endpoint was Magseed retrieval rate. Secondary endpoints were adverse events, accuracy of placement, surgery duration, and positive margin rate. Clinicians were surveyed for ease of use using a Likert scale. Descriptive statistics and Fisher exact test were performed to assess univariable associations with positive margins. RESULTS: There were 124 Magseeds placed including 1 marker in 93 subjects, 2 markers in 11, and 3 markers in 3. The majority of lesions were masses (63%) followed by calcifications (24%). All 124 Magseeds were placed within 10 mm of the target lesion and surgically retrieved with median operative time of 15 minutes (range, 4–47). No device-related adverse events occurred. Of the 98 malignant lesions, 9 had positive margins and 7 of them underwent a second surgery for additional margins. On univariable analysis, age ≤50 (25.0% vs 6.4%, P = 0.04), lesion histology (P = 0.03), and pathologic T stage (P = 0.04) were significantly associated with positive margins. Clinicians rated the Magseed very or fairly easy to use in most cases. CONCLUSIONS: The Magseed system for localization of nonpalpable lesions was effective and safe; all markers were successfully retrieved with margin-negative resections in 91%. This study supports use of Magseed for localization of breast lesions.