Presentation Time: 11:50 AM: Intra-Operative Radiation Therapy (IORT) Using Electronic Brachytherapy in Treatment of Early-Stage Breast Cancer Patients (pts) with Ductal Carcinoma In Situ (DCIS)

Purpose: An institutional review board (IRB)-approved single arm prospective non-randomized multi-institution trial was designed to determine the efficacy and outcome of single fraction IORT at the time of breast conserving surgery for early-stage breast cancer. A subset of this trial included women age > 40 years with biopsy-proven DCIS < 30 mm by pre-operative clinical and radiographic evaluation. Preliminary results of this DCIS pt subset were reviewed. Materials and Methods: Between May 2012 - July 2018, 235 enrolled pts with pre-operative DCIS diagnoses were successfully treated per protocol with lumpectomy plus a single 20 Gy fraction of IORT using disposable balloon electronic brachytherapy technology. Negative margins and cancer free lymph nodes (if tested) were required on final pathology. Protocol allowed for a single post-IORT surgical re-excision to obtain negative margins. DCIS patients who had pre-operative lesions measuring < 30 mm but were found to have lesions > 30 mm on final pathology along with negative margins were kept in this analysis. Data collection included demographics, histopathology, margins, prognostic factors, adjuvant therapy, local recurrence (LR), and survival. Results: Two hundred thirty-five pts (aged 42 - 89, mean 64 years, median 65 years) with biopsy proven DCIS completed IORT treatment per protocol. Mean follow-up was 4 years, with a range of 2 - 8 years. DCIS size on final pathology ranged from 0.1 - 90 mm, median size 12 mm, mean size 11.8 mm. Seventeen pts had a final pathology size of > 30 mm, 7 of these pts requiring a re-excision to obtain final negative margins. Negative margins were obtained on initial lumpectomy in 210 (89%) of 235 pts. Twenty-five (11%) pts required a single re-excision to obtain negative margins. All final margins were cancer free. Estrogen receptor status was positive (ER+) in 152 (88%) of the 173 pts for which it was available. Eighty-seven (37%) pts had high grade tumors. There was no breast cancer related death. There were 11 (4.7%) recurrences (10 LR and 1 axillary recurrence) in this DCIS subset. Of the 11 recurrences, median age was 69 years (range 45 - 83), median DCIS size was 11 mm, mean size 13.7 mm, (range 4 - 30 mm), and 6 (55%) were high grade lesions. No LR was > 30 mm or required surgical re-excision for negative margins following initial lumpectomy and IORT. ER status was positive in 8 (73%) pts with recurrences and unknown in 3. Three (38%) of the ER+ pts were non-compliant with endocrine therapy, including the pt with axillary recurrence. Five pts opted for mastectomy as LR treatment. Conclusions: Two hundred thirty-five DCIS breast cancer pts successfully treated with a single 20 Gy fraction of IORT per protocol using disposable balloon electronic brachytherapy technology in an IRB approved multi-institution study were found to have an acceptable recurrence rate of 4.7% at mean follow-up of 4 years. The recurrence rate observed in this trial is similar to those reported in the prospective randomized TARGIT-A trial, which differs in that TARGIT-A is a risk-adjusted trial with only about 80% of pts receiving single fraction IORT for treatment. The recurrence rate in our trial is comparable to single-arm peer-reviewed IORT published data and traditional DCIS treatments using breast conserving surgery plus whole breast radiation therapy.