ESTRO 2025 - Abstract Book

S1463

Clinical – Mixed sites & palliation

ESTRO 2025

is known about how SBRT efficacy may differ by breast cancer subtype. We evaluated local recurrence (LR) following varied SBRT regimens stratified by breast cancer subtype.

Material/Methods: We evaluated 233 patients with metastatic breast cancer, treated to a total of 320 spinal lesions with 1- or 3-fraction spine SBRT. Inclusion criteria included treatment of a lesion from C1-L5 using 24Gy x 1, 27Gy in 3 fractions, or 30Gy in 3 fractions. All patients underwent spine MRI ≥2 months following SBRT. Patients were excluded if they received prior RT to the same spinal level. Breast cancer subtype, toxicity, survival, and local control data were collected. The luminal subtype was defined as hormone receptor (HR) positive and HER2-negative. LR was defined as radiographic progression on MRI. Results: Median follow-up after SBRT was 26 months. Of 320 spinal lesions treated with SBRT, subtypes included 250 (78%) luminal cases, 34 (11%) triple-positive (HR+/HER2+), 5 (1.6%) HR-/HER2+ and 31 (9.7%) triple-negative (TNBC). A total of 147 lesions (46%) received 27Gy in 3 fractions, 133 (42%) received 30Gy in 3 fractions, and 40 (13%) received 24Gy in 1 fraction. The median overall survival was 47.2 months. The crude grade 3 vertebral body fracture rate was 2.8%. The crude grade 3 myelitis rate was 2.8%. The overall 5-year LR rate was 15%: by regimen, this comprised a 5-year LR of 16% for 27Gy in 3 fractions, 11% for 30Gy in 3 fractions, and 12% for 24Gy in 1 fraction (p=0.8). The 5-year LR differed significantly by histologic subtype: 15% for HR+/HER2-, 15% for HR+/HER2+, 7.2% for TNBC, and 60% for HR-/HER2+ (p=0.003). The 5-year LR did not differ statistically significantly by grade, though absolute event rates were lower for grade 1 (0%) versus higher grade 2 (24%) and grade 3 (14%) lesions (p=0.3). Conclusion: In this large and fully characterized cohort of breast cancer patients treated with spine SBRT, we demonstrate an excellent 5-year local control rate of 85%. Whereas TNBC was associated with the lowest risk of 5-year-LR following SBRT (7.2%), HR-/HER2+ disease had the highest (60%). These findings must be further validated among larger breast cancer cohorts, yet potentially suggest the need for subtype-specific approaches to breast cancer spinal metastases.

Keywords: Spine, SBRT, Breast

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Mini-Oral FINAL RESULTS FROM A PHASE I DOSE ESCALATION STUDY (DESTROY-1) IN STEREOTACTIC REIRRADIATION Francesco Deodato 1,2 , Donato Pezzulla 1 , Savino Cilla 3 , Carmela Romano 3 , Alessia Re 4 , Mara Fanelli 5 , Marica Ferro 1 , Milly Buwenge 6 , Gian Carlo Mattiucci 4,2 , Alessio Giuseppe Morganti 6,7 , Gabriella Macchia 1 1 Radiation Oncology Department, Responsible Research Hospital, Campobasso, Italy. 2 Istituto di Radiologia, Università Cattolica del Sacro Cuore, Roma, Italy. 3 Medical Physics Unit, Responsible Research Hospital, Campobasso, Italy. 4 Radiation Oncology Department, Mater Olbia Hospital, Olbia, Italy. 5 Research Laboratories, Responsible Research Hospital, Campobasso, Italy. 6 Department of Medical and Surgical Sciences (DIMEC), Alma Mater Studiorum-Bologna University, Bologna, Italy. 7 Radiation Oncology, IRCCS Azienda Ospedaliero-Universitaria di Bologna, Bologna, Italy Purpose/Objective: To report the final results of a dose escalation study (Destroy-1) [1] investigating the stereotactic radiotherapy (SBRT) retreatment of recurrences occurring later than 4 months after in-field radiation (RT).