Abstract P3-13-23: Predicting residual disease in breast conservative surgery after neoadjuvant treatments in breast cancer patients using the margin index tool

Background. The appropriate surgical margin after neoadjuvant treatment (NAT) is controversial. Margin index, a relationship of the margin obtained to the size of the tumor, is a reliable method for the prediction of residual disease after breast conservative surgery (BCS) in the adjuvant setting. Our aim was to apply the margin index to patients with BCS after NAT to predict residual disease.

Material and Methods. From a prospectively maintained database, patients with stage I - III with NAT who underwent BCS between July 2008 and December 2012 were included. Margin index was calculated as for the adjuvant setting: margin index = closest margin (mm)/tumor size (mm) × 100 considering the tumor size of the lumpectomy specimen. A receiver operating curve was created using the derived margin index and the presence or absence of residual disease in the re-excision specimen. Patients with pathologic complete response (pCR) (no invasive tumor) were excluded.

Results. Of the 206 patients, 63 (30.5%) had a pCR and were excluded. Of the 143 patients, 76 (53%) had an intraoperative re-excision depending on the surgeon or the intraoperative pathology report. Of the 76 patients, 23 (32%) had residual tumor in the intraoperative re-excision specimen. There were no statistically significant differences in residual disease regardless of who indicates intraoperative re-excision. (p= 0.56) Twenty-three patients (16%) underwent a second surgery for positive or close margins ( < 2mm). Residual disease, whether infiltrating or in situ or both, was found in 10 (43%) patients. The overall c index for the receiver operating curve was 0.76. A margin index > 5 had a sensitivity of 80% and a specificity of 63%.

Conclusion. Rates of re-excision after NAT in BCS patients are similar to the adjuvant setting. Margin index may be a valuable tool for determine residual disease after NAT in patients undergoing BCS. Further validation of this index is warranted in a larger cohort of patients after NAT to confirm these results.

Citation Format: Rubio IT, Loinaz I, Esgueva-Colmenarejo AJ. Predicting residual disease in breast conservative surgery after neoadjuvant treatments in breast cancer patients using the margin index tool [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P3-13-23.

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