950 Comparison of Magseed and Savi Scout Localisation Systems in Wide Local Excision of Non-Palpable Breast Lesions: A Retrospective Cohort Analysis of Surgical Outcomes, Positive Margins, Re-Excision Rates, and Specimen-to-Tumour Size Ratios

Abstract

Aim
This study compares the surgical outcomes of Magseed and Savi Scout localisation systems in wide local excision of non-palpable breast lesions across two hospitals. Factors analyzed include positive margin rates, re-excision rates, specimen volumes, and specimen-to-tumour size ratios.

Method
A retrospective cohort analysis was conducted on 200 lesions (100 localized with Magseed and 100 with Savi Scout). Data were extracted from electronic medical records, including patient demographics, tumour characteristics, and surgical outcomes. Positive margins were defined as tumour cells at the inked margin or within 2 mm for ductal carcinoma in situ (DCIS) and 1 mm for invasive ductal carcinoma (IDC). Statistical analyses evaluated differences in surgical outcomes and specimen-to-tumour size ratios.

Results
Both systems achieved 100% localisation success rates and identical positive margin rates (13%). However, Savi Scout specimens were significantly larger, with a specimen volume-to-tumour size ratio of 5617.06 mm³/mm compared to 3935.78 mm³/mm for Magseed (p < 0.01). Larger specimen volumes correlated with reduced positive margins, with 69% and 92.3% of positive margins occurring at specimen-to-tumour size ratios ≤1.60 and ≤3.50 for Magseed and Savi Scout, respectively. Differences in re-excision rates (Magseed: 10%, Savi Scout: 13%) reflected institutional protocols.

Conclusions
Both localisation systems achieve similar positive margin rates, but Savi Scout's larger specimen volumes may confer a potential advantage in margin clearance. Institutional protocols and tumour types influence re-excision rates. These findings highlight the importance of tailoring localisation methods to surgical and institutional practices.