Abstract PS1-07-01: Outcomes of 1-3 brain metastases treated with stereotaxy in metastatic breast cancer: a single institutional experience from eastern India

Abstract Background Patients with metastatic breast cancer (MBC) behave differently with receptor status.Stereotaxy is recommended in treatment of 1-3 brain metastases usually in patients with disease specific graded prognostic assessment (DS-GPA) calculated median survival time (MST) of more than 6 months. Purpose To assess the outcomes of 1-3 brain metastases treated with stereotaxy in MBC in terms of Time to Progression (TTP) in brain and Overall Survival (OS) along with their relationship with receptor status and DS-GPA. Methods 22 MBC patients (from January 2020 – May 2025) with 1-3 brain metastases with DS-GPA (score 1.5 – 3.5) calculated MST more than 6 months of different receptor status (ER/PD and Her2) treated with stereotaxy 30 Gy/5 fractions were analyzed. Intracranial responses were recorded as per RANO-BM response assessment (Response Assessment in Neruro Oncology Brain Metastases) at 3 months post radiation with MRI of brain. Time to progression (TTP) in brain was calculated as time between completion of radiation to brain and radiologically detectable new brain lesion (in months). Overall survival was calculated as the time between completion of radiotherapy and death of the patient. Acute radiation toxicities were assessed as per RTOG (as per embedded in CTCAE v2.0) criteria. Results 2 patients were lost to follow up at 3 months of RT completion. Complete response (CR) was seen in 6 (30%) patients, partial response (PR) was seen in 12 (60%) patients, while stable disease (SD) and progressive disease (PD) was seen in 1 patient each at 3 months. Patients with ER/PR-positive tumors demonstrated non significant (p = 0.711) longer median time to brain progression (TTP: 14.0 months, 95% CI: 7.07–20.93) compared to ER/PR-negative patients (11.0 months, 95% CI: 2.51–19.49). Her2Neu-positive patients had longer median TTP (16.0 months, 95% CI: 8.42–23.58) compared to Her2Neu-negative (10.0 months, 95% CI: 4.16–15.84), with p = 0.067. Patients with fewer brain metastases (1 lesion) had longer median TTP (15.0 months) and OS (19.0 months) compared to those with 2 (TTP: 16.0; OS: not estimable) or ≥3 lesions (TTP: 6.0; OS: 12.0). Overall survival (OS) was higher in the ER/PR-positive group (median OS: 19.0 months, 95% CI: 7.12–30.88) vs ER/PR-negative (17.0 months, 95% CI: 10.36–23.64; p = 0.653). Median OS was notably higher in the Her2Neu-positive cohort 31.0 months versus 17.0 months for Her2Neu-negative patients (95% CI: 12.84–21.16), p = 0.304. Patients with DS-GPA 3.5 had the most favourable survival (median TTP: 20.0 months; OS: 31.0 months), whereas those with DS-GPA 1.5 had the poorest (TTP: 6.0 months; OS: 7.0 months). Toxicities were more frequent in patients ≥58 years (any grade: 4; grade ≥2: 2) compared to younger patients (3 and 1 respectively). Higher toxicity rates were also observed in ER/PR-positive and Her2Neu-positive groups (grade ≥2 toxicity: 2 in each) versus their negative counterparts (grade ≥2: 1 each). Conclusion The findings of the study suggest a favourable profile for the ER/PR positive subtype and Her2 targetted therapy settings. The findings reaffirm DS-GPA as a prognostic. While these findings are limited by sample size, they warrant attention in treatment planning for older or receptor-positive patients. Citation Format: A. Datta, S. Majumdar, P. Basu, R. Jena. Outcomes of 1-3 brain metastases treated with stereotaxy in metastatic breast cancer: a single institutional experience from eastern India [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 PS1-07-01.