An International Randomized Prospective Trial Comparing a Supine MRI-based Guidance System, The Breast Cancer LocatorTM, to Wire Localization for Breast-Conserving Surgery for Non-palpable Breast Cancer

Background Positive margins after breast-conserving surgery (BCS) require additional surgery, a negative patient experience that also adds costs to care. Pilot trials indicate the Breast Cancer Locator TM (BCL), a novel supine magnetic resonance imaging–based guidance system, helps surgeons resect cancers with a low positive margin rate (PMR). Our objective was to evaluate BCL noninferiority and superiority compared with wire localization (WL) in reducing the PMR with BCS. Methods Patients with nonpalpable, magnetic resonance imaging–visualized invasive breast cancer or ductal carcinoma in situ undergoing BCS were prospectively randomized to either BCL or WL. Results In total, 418 randomized patients underwent surgery. The PMR was 14.4% (30/209) in the BCL group and 21.1% (44/209) in the WL group, a relative decrease of 32%. In primary analysis, the treatment difference was −7.1% (95.4% confidence interval [CI] −14.3 to 0.1). Noninferiority was demonstrated ( p = 0.011). The one-sided p -value for superiority ( p = 0.025) slightly exceeded the prespecified significance level of 0.023. In prespecified analysis stratified by final tumor type, the PMR was significantly lower in the BCL group ( p = 0.019). Fewer BCL patients underwent re-excision: 12.9% versus 19.6%, a relative decrease of 34%. The PMR for all tumor types was lower in the BCL group, with a > 60% relative reduction in PMR in patients with ductal carcinoma in situ (20.6% vs. 53.3% [95% CI −52.1 to −9.1]) and invasive lobular carcinoma (9.1% vs. 25.6% [95% CI −32.9 to −0.2]). Adverse event rates were similar. Conclusions BCL was noninferior to WL and superior in analysis stratified by final tumor type. Clinically meaningful relative reductions in PMR and re-excision rates were observed.