Defining negative margins in DCIS patients treated with breast conservation therapy: The University of Chicago experience.

Management of ductal carcinoma in situ (DCIS) has been evolving and the majority of women are now being treated with breast-conserving surgery and radiation therapy (i.e. breast conservation therapy [BCT]). Controversies still exist regarding the histologic features and margin status that are associated with local recurrence. The goal of this study was to review our institution's experience in patients diagnosed with DCIS and treated with BCT to determine pathologic features that can predict local recurrence, with particular emphasis on the final surgical margin status. We analyzed 103 consecutive patients with DCIS who were treated with BCT between 1986 and 2000. The slides were reviewed to determine the final margin status, type of DCIS, size of DCIS, nuclear grade, presence of necrosis and calcification, and volume of excised specimen. Margins were considered positive when DCIS touched or was transected at an inked margin. Negative margins were further categorized as close (less than 1 mm), 1--5 mm, and more than 5 mm. The size of the DCIS was determined based on either the maximal dimension on a slide or from the number of consecutive slides containing DCIS. Morphology and immunohistochemical profiles of the recurrent DCIS cases were compared with original DCIS. All patients were treated uniformly with external beam radiation therapy to the entire breast (median dose 46 Gy) with a boost to the tumor bed (median dose 14 Gy). The median follow-up was 63 months (range 7--191 months). The actuarial 5-year local control rate was 89%. The median time to local recurrence was 55 months. There were 13 local recurrences, of which 9 recurred as pure DCIS and 4 as invasive ductal carcinomas. Univariate analysis showed a significant association with local recurrence for positive margin (p=0.008), high nuclear grade (p=0.02), and young age at diagnosis (p=0.03). If margins were negative, the 5-year local control was 93%, as compared to 69% if margins were positive. A multivariate analysis showed that early age at diagnosis, positive margin status, and high nuclear grade were independently associated with local recurrence. The morphology and immunohistochemical stains of all nine recurrent DCIS were similar to those of the original DCIS. Breast conservation can be achieved with excellent local control by obtaining microscopically negative margins as strictly defined by DCIS not touching the inked surgical margins, and postoperative radiation that includes boost therapy to the tumor bed.