Should Ductal Carcinoma-in-situ (DCIS) Be Removed from the ASTRO Consensus Panel Cautionary Group for Off-protocol Use of Accelerated Partial Breast Irradiation (APBI)? A Pooled Analysis of Outcomes for 300 Patients with DCIS Treated with APBI

To analyze outcomes in patients with ductal carcinoma-in-situ (DCIS) treated with accelerated partial breast irradiation (APBI) within a pooled set of patients. A total of 300 women with DCIS underwent APBI between April 1993 and November 2010 as part of American Society of Breast Surgeons MammoSite Registry Trial (n = 192) or at William Beaumont Hospital (n = 108). Patients with pure DCIS < 3 cm (n = 125) were assigned to the cautionary risk group per American Society of Radiation Oncology consensus panel guidelines for off-protocol use of APBI and analyzed compared to a pooled invasive suitable (n = 653) risk group and pooled invasive suitable/cautionary (n = 1,298) risk group. The rate of ipsilateral breast tumor recurrence (IBTR) for all 300 DCIS patients was 2.6 % at 5 years with no regional recurrences, while cause-specific survival was 99.5 % and overall survival (OS) was 96.4 %. When comparing the cautionary DCIS group to the invasive suitable/cautionary group, no difference in IBTR was noted (2.6 vs. 3.1 %, P = 0.90) with significant improvements in distant metastases (0 vs. 2.5 %, P = 0.05), disease-free survival (98.5 vs. 94.4 %, P = 0.05), and OS (95.7 vs. 90.8 %, P = 0.03) noted for DCIS patients. When comparing cautionary DCIS patients to invasive suitable patients, no difference in IBTR were noted (2.6 vs. 2.4 %, P = 0.76), while improved OS for DCIS patients was noted (95.7 vs. 90.9 %, P = 0.02). This analysis of the largest cohort of patients with DCIS treated with APBI supports previously reported excellent outcomes; as a result of small numbers of events, further data are necessary to confirm these findings.