Single fraction based-partial breast irradiation: 10-year results of the SiFEBI phase 2 prospective trial

Purpose: This analysis updates the SiFEBI phase 2 trial (NCT01727011) evaluating accelerated partial breast irradiation (APBI) delivered as a single fraction (sfPBI) of postoperative multicatheter interstitial HDR brachytherapy (MIB) in elderly patients with low-risk breast cancer. Materials and methods: Patients aged ≥ 70 years (Balducci I-II) with low-risk breast cancer were enrolled. After lumpectomy, intraoperative catheter implantation was performed and postoperative sfPBI (16 Gy) was delivered. The primary endpoint was cumulative incidence of local recurrence (ciLR). Secondary endpoints included cumulative incidence of distant metastasis (ciDM), cancer-specific survival (CSS), overall survival (OS), late toxicity, cosmetic outcome, and endocrine-therapy (ET) adherence. Results: From 11/12 to 09/14, 26 patients were enrolled. Median age was 76.6 years; median tumour size was 10.4 mm. Most tumours were invasive ductal carcinoma (76.5%), all of luminal subtype. After a median follow-up of 137 months, 10-year ciLR was 5%. Ten-year ciDM, CSS, and OS were 0%, 100%, and 81%, respectively. Late toxicity was observed in 9 patients (34.6%) with a total of 12 events (G1: 83.3%, G2: 16.6%). Reported late effects included breast pain, hypopigmentation, telangiectasia and breast fibrosis. Ten-year cosmetic outcomes were reported in 18 pts as excellent in 14 patients (77.8%) and good in 4 patients (22.2%). Median ET duration was 59 months; 14 pts (53.8%) were non-adherent. Conclusion: In this elderly, low-risk cohort, single fraction postoperative MIB sfPBI provided excellent long-term oncological outcomes with acceptable toxicity and cosmesis. Larger studies with extended follow-up are warranted.