Phase 2 Trial of Ultrahypofractionated Image-guided Partial Breast Irradiation Following Lumpectomy with Optional Oncoplastic Reconstruction for Early-stage Breast Cancer.

Purpose: As accelerated partial breast irradiation is gaining widespread acceptance for low-risk breast cancers treated with breast conservation, its role following oncoplastic surgery remains controversial. Methods and Materials: We performed a prospective phase 2 trial of women aged 50 and older who were estrogen receptor positive with stage 0 to 1 breast cancer measuring ≤3 cm following successful lumpectomy with optional oncoplastic reconstruction. Patients were treated on the Varian Edge radiosurgery system to a prescribed dose of 30 Gy in 5 fractions, and the primary endpoints were feasibility and safety. Patient-reported cosmesis was assessed using the Breast Cancer Treatment Outcome Scale validated instrument. Results: From 2018 to 2022, 50 patients with 52 tumors with a median age of 76 were enrolled, including 79% invasive breast cancer with 48% undergoing oncoplastic reconstruction. With a median follow-up of 47 months, long-term patient-reported cosmesis was excellent in 89% of patients and good in 11% of patients. All patients were locally controlled, but there were 2 ipsilateral breast events consisting of an intramammary lymph node failure and second primary triple-negative breast cancer outside the radiation field, both successfully salvaged with further local and systemic therapy. Conclusions: In carefully selected patients with low-risk early-stage breast cancer, patients treated with a 5-fraction regimen of partial breast irradiation achieve excellent cosmetic and oncological outcomes. Oncoplastic reconstruction was not a contraindication to partial breast irradiation.