Factors Associated With Residual Disease on Re-Excision Specimens After Breast-Conserving Surgery for Breast Cancer.

[BACKGROUND] After breast-conserving surgery (BCS) for early-stage breast cancer, re-excision rates for positive or close margins remain high, although most re-excisions show no residual disease. This study aimed to identify clinicopathologic factors associated with residual disease to guide re-excision decisions.

[METHODS] The study evaluated women with ductal carcinoma in situ (DCIS) or invasive breast cancer who underwent BCS and re-excision for positive or close margins from 2018 to 2024 at the Saint John's Cancer Institute. The association between clinical-pathologic variables and residual disease was evaluated by multivariable logistic regression.

[RESULTS] Of 932 patients treated with BCS, 184 (19.7 %) underwent re-excision for positive or close margins. Residual disease was found in 54 (29 %) patients, most commonly DCIS (n = 36, 66.7 %). In the multivariable analysis, residual disease was associated with three or more positive margins (odds ratio [OR], 9.87; 95 % confidence interval [CI], 3.23-30.17), DCIS at the margin (OR, 7.4; 95 % CI, 1.56-35.16), PR negativity (OR, 4.06; 95 % CI, 1.26-13.12), and mammographic microcalcifications (OR, 3.0; 95 % CI, 1.17-7.69). Conversely, reduced risk was associated with age ≥60 years (OR, 0.07; 95 % CI, 0.01-0.46), invasive carcinoma with extensive intraductal component (EIC: OR, 0.15; 95 % CI, 0.03-0.66), and pure DCIS (OR, 0.14; 95 % CI, 0.03-0.63).

[CONCLUSIONS] Residual disease was found in fewer than one third of re-excision specimens. Factors reflecting margin burden and tumor biology, especially the number of positive margins, DCIS involvement of margin, and PR-negativity, were associated with residual malignancy, whereas EIC and older age were associated with a lower likelihood of residual disease. These findings support a risk-adapted, individualized approach to re-excision after BCS to minimize unnecessary surgery.