Abstract P1-20-07: Do surgical margins matter after mastectomy? A meta-analysis of 37,738 breast cancer patients in 33 studies

Abstract Background: Leaving involved margins after mastectomy for breast cancer has been associated with an increased risk of local recurrence. Current guidelines endorse a policy that negative margins of no ink on tumour represent sufficient margin for local control and that the routine practice of obtaining a more widely negative margin is not indicated. We performed a systematic review of the literature and meta-analysis of studies analysing the impact of margin involvement after mastectomy on subsequent local recurrence. Methods: A systematic review was carried out searching MedLine, EmBase and ProQuest databases using the terms ‘mastectomy’, ‘resection margin’, ‘deep margin’, ‘margin status’ ‘fascia’ and ‘muscle invasion or infiltration’ from 1980 - 2019. In total 2,199 papers were screened and 33 studies were included in the quantitative synthesis. Statistical Methods: Meta-analysis was conducted using random effects modelling, pooling hazard ratios (HR), and odds ratios (OR) from binary outcome data. The associations between positive margins and local recurrence were stratified by positive margin distance and analysed according to use of adjuvant radiotherapy and follow up duration. Results: In total 37,738 patients, with a median age of 54.5 years, were included in the quantitative synthesis. Positive margins were associated with increased local recurrence on univariable analyses (HR 2.99, 95%CI: 2.99, 2.15 - 4.15), multivariable adjusted analyses (HR, 2.61, (95%CI 2.03-3.35) (which included Molecular Phenotype, Stage and Node status) as well as binary outcome data (OR, 95%CI: 2.75, 1.94-3.88). Positive margins were consistently associated with increased local recurrence, regardless of the distance of the tumour from the margin defined as positive (HR, 95%CI, tumour at ink: 2.39, 1.53-3.72; margin <1mm: 3.08, 1.60-5.93; margin <2mm: 2.63, 1.86-3.74; margin <5mm: 7.09, 1.32-38). The odds ratio of local recurrence with positive margins increased with follow-up time of >5 years compared to <5 years (OR <5years: OR 2.15, 1.14 - 3.27 to OR >5 years OR 3.50, 2.13 - 5.75). Data were available from five studies for patients not receiving radiotherapy. In this subgroup positive margins were associated with a 3-fold risk of local recurrence (OR: 3.01, 1.96-4.61). Conclusions: On meta-analysis the risk of local recurrence after mastectomy is associated with margin proximity. Most data on margin status has related to breast conserving surgery. Adequate surgical margin clearance greater than 2mm margin after mastectomy is required to prevent local recurrence and International guidelines should reflect this finding. Citation Format: James Bundred, Sarah Michael, Sarah Bowers, Nicola Barnes, David Dodwell, Yasmin Jauhari, Nigel Bundred. Do surgical margins matter after mastectomy? A meta-analysis of 37,738 breast cancer patients in 33 studies [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P1-20-07.