Surgical and Oncologic Impact of Cavity Shave Margins in Breast-Conserving Surgery.

BACKGROUND: Surgical margin status is a critical determinant of local control in breast-conserving surgery (BCS). Circumferential cavity shave margins (CSM) reduce positive margin rates and re-excisions, but their impact on recurrence remains incompletely defined. METHODS: We conducted a retrospective cohort study of patients undergoing BCS for stage 0-III breast cancer within a single integrated health system between 2017 and 2022. Patients were stratified according to operative technique into those undergoing BCS with circumferential CSM and those undergoing BCS without (non-CSM). The primary oncologic endpoint was recurrence; the secondary outcome was re-excision for a positive margin. Multivariable logistic regression identified factors independently associated with recurrence. RESULTS: A total of 2,648 patients met inclusion criteria, including 1762 (66.5%) treated with non-CSM and 886 (33.5%) with CSM. Adoption of CSM increased progressively over the study period. Re-excision for positive margins was significantly lower in the CSM cohort (7.3% vs. 19.2%, p < 0.001). Overall, 122 relapses (4.6%) were documented. Recurrence was observed in 3.5% of patients undergoing CSM and 5.2% treated with non-CSM, although this difference did not reach statistical significance (p = 0.067). On multivariable analysis, CSM was not independently associated with recurrence, whereas higher clinical stage and omission of radiotherapy remained significant predictors. CONCLUSIONS: Although CSM was not independently associated with recurrence after adjustment, routine CSM substantially reduced re-excision for positive margins. Reducing the need for subsequent surgical procedures may lessen patient burden while improving healthcare utilization and lowering associated costs, supporting CSM as a valuable strategy in contemporary BCS.