J. Hanna1, D. Lannin1, M. Butler1, A. B. Chagpar1 1Yale University,Surgery,New Haven, CT, USA
Introduction: Recent randomized controlled trials have demonstrated that taking cavity shave margins in women undergoing partial mastectomy (PM) results in a halving of positive margin and re-excision rates. We sought to determine whether taking a ‘mini-shave’, or a tiny sample of each margin, would similarly reduce the positive margin rate, while removing less tissue.
Methods: A retrospective cohort study was performed of patients undergoing PM with mini-shave excision of margins between October 21, 2011 and November 22, 2013. Patient demographics and clinicopathologic tumor features were collected, along with margin status and volume of tissue excised from the primary PM specimen as well as the mini-shaves. A positive margin was considered to be no tumor at ink for invasive cancer and tumor within < 1 mm for DCIS. Statistical analyses were performed using SPSS Version 21 software.
Results: There were 121 patients in the cohort of interest. The median patient age was 62. 21 (17.4%) had invasive cancer, 31 (25.6%) had DCIS, and 69 (57.0%) had both. The median size of invasive cancer was 1.3 cm, and the median size of DCIS was 1.2 cm. 8 (6.6%) patients had invasive lobular cancer, and 3 (2.5%) had neoadjuvant chemotherapy. The median volume of the initial PM specimen was 85.8 cm3, and 27 (22.3%) had initially positive margins. While the same number of patients (27, 22.3%) also had additional tissue removed intraoperatively prior to mini-shave excision, only 7 (25.9%) of these had positive margins on their PM specimen. Selective excision of additional tissue did not significantly reduce the positive margin rate (22.3% to 19.8%, p=0.250 by McNemar test). All but one patient had mini-shaves taken from all six faces; the median total volume of mini-shaves excised per patient was 1.3 cm3. The median ratio of mini-shave:PM surface area was 0.03. The mini-shaves were negative in all but 4 patients, resulting in a reduction of the positive margin rate from 19.8% to 3.3%, p<0.001. Six patients underwent re-excision; three of whom had a mastectomy. 5 (83.3%), including the two who had negative mini-shaves, were found to have residual cancer. All five had DCIS and one had invasive cancer; the median size of the residual disease was 1.6 cm.
Conclusion: Taking mini-shaves at the time of PM results in an 83% reduction in positive margin rates. However, mini-shaves sample only 3% of the surface area of the initial cavity, and therefore may not accurately reflect the presence or absence of residual disease. It is unclear whether this potential sampling error will affect recurrence rates, particularly in the current era of nearly ubiquitous adjuvant systemic and radiation therapy.