Cavity shave margins (CSM) cut positive margins/re-excisions but do not improve DFS or OS at ~5 years in Stage 0–III breast cancer (SHAVE + SHAVE2 pooled).

In the pooled SHAVE (single-center) and SHAVE2 (9-site US) randomized trials (n=631; Stage 0–III planned partial mastectomy; median follow-up 60.4 months), patients were intraoperatively randomized after standard partial mastectomy to routine cavity shave margins (≥4 faces) vs no additional shaves. CSM reduced post-randomization positive margins (14.0% vs 34.8%, p<0.001), re-excisions (9.2% vs 24.1%, p<0.001), and final positive margins after any re-excision (6.3% vs 15.8%, p<0.001), while local recurrence was essentially identical (1.3% vs 1.6%, p=1.000) and 5-year DFS (91.9% vs 92.6%, p=0.820) and OS (93.5% vs 93.5%, p=0.841) did not differ. This lands where modern breast-conserving therapy already performs with guideline-based margin standards (“no ink on tumor” for invasive cancer) and high radiation use—i.e., CSM meaningfully improves surgical quality metrics (fewer positive margins/re-ops) but doesn’t move survival in a setting where adjuvant RT/systemic therapy largely drives recurrence and survival outcomes (trial IDs: NCT01452399; NCT02772731).