Purpose: Breast-conserving therapy (BCT) is an accepted method of treating early breast cancer. We hypothesized that routine excision of additional cavity shave margins (CSM) at time of initial partial mastectomy reduces the need for additional surgery. Methods: A single-institution retrospective review was performed of women, 18 years or older, with a new diagnosis of breast cancer who underwent partial mastectomy between 1 January 2004 and 1 October 2009. Five hundred thirty-three charts were reviewed. Of those, 69 patients underwent CSM at time of initial operation. These 69 patients were matched with patients who had undergone partial mastectomy without CSM by tumor size, presence of extensive intraductal component, and primary histology. Results: The two groups were well matched for age, nuclear grade, associated lymphovascular invasion (LVI), receptor status, and multifocality. We found that 31.9% (44/138) required return to the operating room (OR) for re-excision of margins. Rate of return to the OR was 21.7% (15/69) in the CSM group and 42.0% (29/69) in the matched group (p = 0.011). Multivariate analysis found factors significantly associated with need for additional operation included lack of CSM (odds ratio 9.2, 95% CI 2.8-30.5, p = 0.0003), larger extent of intraductal component (odds ratio 7.0, 95% CI 1.8-27.0, p = 0.005), and lack of directed re-excision (odds ratio 6.4, 95% CI 1.7-25.1, p = 0.007). Conclusions: CSM at time of initial partial mastectomy decreases rate of re-excision by as much as ninefold. CSM should be considered at time of initial operation to reduce the need for subsequent reoperation.
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