Long-Term Results of a Phase 2 Prospective Clinical Trial of Single-Fraction, High-Gradient Adjuvant Partial Breast Irradiation in Early-Stage, Hormone-Positive Breast Cancer

Abstract

Purpose: This study evaluates the long-term outcomes of single-fraction, high-gradient partial breast irradiation (BreaStBRT) as a postoperative treatment in patients with early-stage, hormone-positive breast cancer. It aims to assess acute and late treatment-related toxicity, cosmesis, patient-reported quality of life (QoL), and oncologic outcomes.

Methods and materials: This single-institution, single-arm, phase 2 prospective trial included postmenopausal women ≥50 years with early-stage, hormone-positive breast cancer treated with breast-conserving therapy followed by BreaStBRT. Patients were treated in a single-fraction with a high-gradient by delivering a dose of 15 to 22 Gy to the surgical bed with a steep fall-off to a minimum of 5 Gy to a 1 cm isometric expansion from the surgical bed; most patients were treated with magnetic resonance imaging-guided radiation therapy. Primary endpoints included acute and late toxicity and 5-year ipsilateral breast tumor recurrence. Secondary endpoints included regional-nodal recurrence, distant metastasis, mastectomy-free survival, and overall survival, along with patient-reported cosmesis and QoL assessments.

Results: Fifty patients were treated between 2015 and 2018. Median follow-up was 78 months. Acute and late radiation-related toxicities were observed in 44% and 68% of patients, respectively; no acute grade 3 or higher toxicities were reported, and one instance of late grade 3 fibrosis was observed. Five-year ipsilateral breast tumor recurrence, mastectomy-free survival, and overall survival were 4%, 98%, and 92%, respectively. Cosmesis was rated as good to excellent in over 90% of cases by both patients and physicians through a 5-year follow-up. QoL assessments showed stable global health, physical functioning, sexual functioning, and body image results through follow-up.

Conclusions: BreaStBRT provides promising oncologic outcomes and favorable long-term cosmesis and QoL results with a low rate of treatment-related toxicity. This convenient regimen offers a viable alternative for carefully-selected early-stage, hormone-positive breast cancer patients. Further comparative trials are warranted to solidify the role of BreaStBRT in clinical practice.