Phase II Study of Preoperative Stereotactic Ablative Body Radiotherapy for Early-Stage Breast Cancer: Introduction of a Novel Form of Accelerated Partial Breast Radiotherapy
Mené entre 2017 et 2019 sur 20 patientes atteintes d'un cancer du sein HR+ de stade précoce (âge médian : 65 ans ; durée médiane de suivi : 14 mois), cet essai de phase II évalue l'efficacité, du point de vue du taux de réponse complète, et la toxicité d'une radiothérapie stéréotaxique d'ablation avant la chirurgie
Background: Pre-operative delivery of partial breast irradiation (PBI) facilitates smaller target volumes and reduced dose to normal tissues. We hypothesized that pre-operative stereotactic ablative radiotherapy (SABR) delivered to intact breast tumor would achieve pathological complete response (pCR) in 25% of patients while preserving low rates of toxicity and good cosmesis. Methods: Eligible patients had hormone receptor-positive, clinically node-negative breast cancer measuring ≤2cm on magnetic resonance imaging (MRI). Patients received SABR to 28.5 Gy in three fractions of 9.5 Gy to the tumor defined on MRI and computed tomography in the prone position. Lumpectomy was performed 6-8 weeks later. Tumor pathologic response was assessed and adverse events (AEs) were rated on the Common Terminology Criteria for AEs version 4.0 scale. Physician-rated cosmesis are also reported. Results: Twenty patients were enrolled and completed treatment; the study was terminated prior to full accrual due to pre-specified stopping rules. Median follow-up was 14 months. Median patient age was 65 years (range 54-78) and median tumor size on MRI was 10.5mm (range 5-22). All patients had negative surgical margins. Four patients (20%) required post-operative whole breast and axillary radiation due to positive sentinel lymph nodes. No pCR were observed, although the median percent residual tumor cellularity was 30% (range 10-80) and 90% had ≤50% residual cellularity. Three patients had late grade 3 AEs, including 2 of the 4 patients who received post-operative RT. Cosmesis was good in 85% of cases, fair in 10%, and poor in 5%. Conclusion: We observed a 0% incidence of pCR with pre-operative SABR for early-stage BrCa as evaluated 6-8 weeks following treatment. Evolution of pCR may require longer than 6-8 weeks. Patients requiring post-operative whole breast radiotherapy after pre-operative SABR may be at increased risk for high-grade soft tissue toxicity. Further studies are needed to determine optimal patient selection, treatment methodology and timing of pathologic response evaluation.
International Journal of Radiation Oncology, Biology, Physics 2023