Abstract PS1-09-04: A study of curative approach treatment along with metastasis-directed SBRT in bone-only oligometastatic breast cancer patients

Abstract Purpose and Objectives: A combination of metastasis-directed ablative therapy and curative intent treatment for OMBC is an active area of research. We designed this prospective study to include a homogenous population of oligometastatic breast cancer patients with bone-only metastases. Materials and Methods: Patients with 1-5 bone only metastasis were included and received SBRT to the metastatic site followed by curative intent anthracycline and taxane based chemotherapy followed by surgical excision of the primary tumor. Patients with spinal metastasis received 30 Gy in 3 fractions over 3 days and non-spinal metastasis received 24Gy in 2 fractions over 2 days. Response assessment was done using PERCIST criteria. Results: Between June 2021 and April 2024, a total of 49 patients with a total of 84 metastatic sites were enrolled. After a median follow-up of 19.4 months (1.1-44.4 months), median PFS was 18.8 months (1.1-44.4 months) 95% CI 26.512-36.349, while the 1 and 2-year PFS were 81.63% and 71.43%, respectively. Local control at metastatic sites was 92.4% at first follow-up, and 97.9% had a complete metabolic response at last follow-up. Multivariate analysis for PFS showed patients who completed NACT (p-value: 0.05) and underwent surgical excision of the primary (p-value: 0.02) had significantly improved PFS, and hormone receptor positivity reached near significance (p-value: 0.07). Median OS for the entire cohort was 19.4 months (1.56-44.4 months), while the 1 and 2-year OS were 89% and 74%, respectively. Multivariate Analysis for OS revealed significantly improved OS for patients completing NACT (p-value:0.01), receiving LRRT (p-value:0.038), and presence of vertebral metastasis (p-value: 0.038). With SBRT, 96.4% of patients showed a decrease in pain medication step and requirement. The median time to pain response was 2.3 months (1.0-4.7 months). No Grade 3-4 toxicities were documented till last follow-up. Pain flare was the most common toxicity observed in 10.7% of the patients. Conclusion: Oligometastatic breast cancer is a very heterogeneous group of patients. Our study shows excellent outcomes in treatment-naïve, bone-only metastatic patients, emphasizing the need for patient selection. Citation Format: A. Dagar, A. Ghosh, A. Singhal, A. Amritt, J. Sharma, A. Kumar, A. Sharma, A. Batra, P. Patil, S. Saini, A. Mishra, S. Deo, A. Gogia, D. Sharma, S. Mallick. A study of curative approach treatment along with metastasis-directed SBRT in bone-only oligometastatic breast cancer patients [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS1-09-04.