Targeted Intraoperative Radiotherapy for the Management of Ductal Carcinoma In Situ of the Breast.

Multiple long-term studies have demonstrated a propensity for breast cancer recurrences to develop near the site of the original breast cancer. Recognition of this local recurrence pattern laid the foundation for the development of accelerated partial breast irradiation (APBI) approaches designed to limit the radiation treatment field to the site of the malignancy. However, there is a paucity of data regarding the efficacy of APBI in general, and intraoperative radiotherapy (IORT), in particular, for the management of ductal carcinoma in situ (DCIS). As a result, use of APBI, remains controversial. A prospective nonrandomized trial was designed to determine if patients with pure DCIS considered eligible for concurrent IORT based on preoperative mammography and contrast-enhanced magnetic resonance imaging (CE-MRI) could be successfully treated using IORT with minimal need for additional therapy due to inadequate surgical margins or excessive tumor size. Between November 2007 and June 2014, 35 women underwent bilateral digital mammography and bilateral breast CE-MRI prior to selection for IORT. Patients were deemed eligible for IORT if their lesion was ≤4 cm in maximal diameter on both digital mammography and CE-MRI, pure DCIS on minimally invasive breast biopsy or wide local excision, and considered resectable with clear surgical margins using breast-conserving surgery (BCS). Postoperatively, the DCIS lesion size determined by imaging was compared with lesion size and surgical margin status obtained from the surgical pathology specimen. Thirty-five patients completed IORT. Median patient age was 57 years (range 42-79 years) and median histologic lesion size was 15.6 mm (2-40 mm). No invasive cancer was identified. In more than half of the patients in our study (57.1%), MRI failed to detect a corresponding lesion. Nonetheless, 30 patients met criteria for negative margins (i.e., margins ≥2 mm) whereas five patients had positive margins (<2 mm). Two of the five patients with positive margins underwent mastectomy due to extensive imaging-occult DCIS. Three of the five patients with positive margins underwent successful re-excision at a subsequent operation prior to subsequent whole breast irradiation. A total of 14.3% (5/35) of patients required some form of additional therapy. At 36 months median follow-up (range of 2-83 months, average 42 months), only two patients experienced local recurrences of cancer (DCIS only), yielding a 5.7% local recurrence rate. No deaths or distant recurrences were observed. Imaging-occult DCIS is a challenge for IORT, as it is for all forms of breast-conserving therapy. Nonetheless, 91.4% of patients with DCIS were successfully managed with BCS and IORT alone, with relatively few patients requiring additional therapy.