Predictors of residual disease after breast-conserving surgery.

168 Background: Locoregional failure after breast conserving surgery (BCS) is often due to undetected residual disease, and the risk of such residual disease frequently guides management. We sought to determine clinical and pathologic factors correlating with the finding of residual invasive cancer and/or DCIS in patients undergoing BCS. Methods: We performed a retrospective cohort study for all invasive and in situ breast cancer treated with BCS at a single institution in 2009. The main outcome variable of interest was residual disease determined by pathologic examinations of cavity shave margins or reexcision. Chart review and statistical analyses were performed to evaluate clinical and pathological factors correlating with residual DCIS or invasive cancer. Results: 256 in situ or invasive breast cancers were treated with BCS in 2009. Of these, 207 (80.9%) underwent additional resection either for close margins or as routine practice. These formed the cohort of interest for this study. 39 patients (18.8%) had residual DCIS and 22 (10.6%) had residual invasive disease. Age, race, histology, ER, PR, her-2-neu and margin distance for invasive disease did not predict the finding of residual DCIS nor invasive cancer. Lymphovascular invasion, while not predicting residual DCIS, was correlated with the finding of residual invasive disease (28.0% vs. 7.9%, p=0.007). Margin distance for DCIS was not predictive of residual invasive cancer but was predictive of residual DCIS. 33.8% of lesions with DCIS margins <1mm were associated with residual DCIS, while 3.4% of those with DCIS margins >5mm were associated with residual in situ disease (p=0.002). Increasing tumor size for invasive and in situ disease were associated with residual DCIS (median 19.5 vs. 13.0 mm, p=0.001 and 22.5 vs. 15.0 mm, p<0.001, respectively); however, neither size component was associated with residual invasive disease. Conclusions: While margin distance and tumor size are associated with residual DCIS in patients undergoing BCS, these are not correlated with residual invasive disease. Conversely, the finding of lymphovascular invasion predicts residual invasive cancer, but not DCIS. These factors may aid in risk stratification of patients and guide postoperative management.