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

Purpose: This study evaluates the long-term outcomes of single-fraction, high-gradient partial breast irradiation (BreaStBRT) as a post-operative 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.

Materials And Methods: Single-institution, single-arm, phase II prospective trial included post-menopausal women ≥50 years old with early-stage, hormone-positive breast cancer treated with breast-conserving therapy (BCT) followed by BreaStBRT. Patients were treated in a single-fraction with a high-gradient by delivering a dose of 15-22 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 MRI-guided radiation therapy. Primary endpoints included acute and late toxicity and 5-year ipsilateral breast tumor recurrence (IBTR). Secondary endpoints included regional-node recurrence, distant metastasis, mastectomy-free survival (MFS), and overall survival (OS), 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. 5-year IBTR, MFS, and OS were 4%, 98%, and 92%, respectively. Cosmesis was rated as good to excellent in over 90% of cases by both patients and physicians through 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.