TP8.1.10 Factors predicting residual disease on re-excision after breast conserving surgery

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Abstract Introduction Breast conserving surgery is the standard of care for early breast cancer, however in a quarter of patients, satisfactory margins are not achieved, usually leading to re-excision. Residual disease is found in less than half of these re-excisions, leading to increased morbidity,poorer cosmesis and increased cost with no oncological benefit. Our study aimed to identify a group of patients with unsatisfactory margins but a low risk of residual disease, who may be able to avoid re-excision. Methods All patients from our unit undergoing re-excision for unsatisfactory margins after breast conserving surgery between January 2013 and October 2019 were identified. Pathological factors predicting residual disease were investigated using univariable and multivariable analysis. Results 220 patients were included. 90 (41%) had residual disease in the re-excision specimen. Residual disease was more likely in those having mastectomy than cavity shaves (61% vs 32%, p < 0.0001). Residual disease increased in a linear fashion with number of involved margins and with increasing tumour size. Tumour size <20mm (p = 0.045), a pathological to radiological tumour size ratio less than 1.5 (p < 0.0001) and disease-free cavity shaves taken at initial surgery (p = 0.041) were all significant predictors of a low chance of residual disease on multivariable analysis. Patients with all three factors had a 14% chance of residual disease. Conclusions More than half of patients undergo unnecessary re-excision, and patients with small, radiologically obvious tumours are less likely to have residual disease. The decision on re-excision should include these factors in addition to the margin status.