Background: Historically, multiple ipsilateral breast cancer (MIBC) has been a contraindication to breast-conserving therapy (BCT). We report the feasibility of BCT in MIBC from the ACOSOG Z11102 trial [Alliance], a single arm noninferiority trial of BCT for women with two or three sites of malignancy in the ipsilateral breast. Methods: Women who enrolled preoperatively in ACOSOG Z11102 were evaluated for conversion to mastectomy and need for reoperation to obtain negative margins. Characteristics of women who successfully underwent BCT and those who converted to mastectomy were compared. Factors were examined for association with the need for margin reexcision. Results: Of 198 patients enrolled preoperatively, 190 (96%) had 2 foci of disease. Median size of the largest tumor focus was 1.5 (range 0.1–7.0) cm; 49 patients (24.8%) had positive nodes. There were 14 women who underwent mastectomy due to positive margins, resulting in a conversion to mastectomy rate of 7.1% (95% confidence interval [CI] 3.9–10.6%). Of 184 patients who successfully completed BCT, 134 completed this in a single operation. Multivariable logistic regression analysis did not identify any factors significantly associated with conversion to mastectomy or need for margin reexcision. Conclusions: Breast conservation is feasible in MIBC with 67.6% of patients achieving a margin-negative excision in a single operation and 7.1% of patients requiring conversion to mastectomy due to positive margins. No characteristic was identified that significantly altered the risk of conversion to mastectomy or need for reexcision. ClinicalTrials.gov Identifier: NCT01556243.
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