Tri-APBI: Single-Institution Phase I/II Prospective Clinical Trial of 3-Fraction Accelerated Partial Breast...

This study aims to report safety, feasibility, toxicity, cosmetic, and quality-of-life (QOL) outcomes of a single-institutional prospective phase I/II clinical trial evaluating a novel 3-fraction accelerated partial breast irradiation (Tri-APBI) regimen.

From August 2018 to March 2021, 75 patients with low-risk hormone-sensitive, human epidermal growth factor receptor 2 (HER-2)-negative breast cancer were enrolled on Tri-APBI, delivered with high-dose-rate (HDR) brachytherapy (22.5 Gy in 3 fractions) or external beam radiation therapy (EBRT) (25.5 Gy in 3 fractions) over 2 to 3 days. Modality was chosen by the treating physician. Planning target volume for all patients was created using a 1-cm expansion of breast tissue around the surgical bed, limited by 0.5 cm from the skin surface.

Stage I disease was present in 79%, whereas the remainder had ductal carcinoma in situ. Tri-APBI was delivered with EBRT in 44 patients (59%) and HDR in 31 (41%). At a median follow-up of 49 months (IQR, 42-55 months), there were 2 ipsilateral breast tumor recurrences, cumulatively 2.6%, both successfully salvaged. There were no axillary or distant recurrences. There was no Common Terminology Criteria for Adverse Events (CTCAE) v4.0 grade 2+ toxicity observed. Good-to-excellent pretreatment cosmesis was present in 94% and 99% by patient and physician rating, respectively, and in 91% and 98% at the latest follow-up. Quantitative cosmesis assessed by percentage of breast retraction assessment (pBRA) showed that breast asymmetry did not worsen compared with pretreatment, with a baseline mean pBRA of 8.1% (CI, 4.1%-12%) and a 24-month mean pBRA of 6.1% (CI, 4.0%-8.1%). Tri-APBI did not negatively impact most domains of patient-reported QOL, except breast symptom burden at 48 and 60 months and sexual functioning at 36 months only.

Tri-APBI as delivered with EBRT or HDR in this trial was feasible and well-tolerated, with low ipsilateral breast tumor recurrence rates at 4 years and minimal impact on patient-reported QOL, qualitative, and quantitative cosmesis. Further follow-up is needed to evaluate long-term oncologic efficacy.