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

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.

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.

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.

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.