Treatment Patterns and Outcomes of Metastatic Breast Cancer Patients with Brain-Only Metastases: A Single-Center Analysis

Summary: Breast cancer patients with brain-only metastatic disease present unique clinical challenges. Our previous study showed that metastatic breast cancer patients with isolated brain metastases (BM) were younger and had significantly longer overall survival (OS) compared to overall breast cancer BM cohorts. There is limited data to guide clinical decision making for this patient population. The present study aims to analyze our institutional experience and clinical outcomes in metastatic breast cancer patients with brain-only metastatic disease. Breast cancer patients with isolated synchronous or metachronous BM were included. Demographics, receptor profiles of primary and BM, and treatment details were collected. Survival analysis was performed using the Kaplan-Meier method to calculate intracranial progression-free survival (PFS), extracranial PFS, leptomeningeal disease (LMD) PFS, and OS. In our institutional database of 232 patients with breast cancer BM diagnosed between January 2017 and July 2024, 30 (12.9%) patients were diagnosed with brain-only metastatic disease. The median age was 50.5 years (range, 32–74). Twenty-seven (90%) patients had previous non-metastatic breast cancer with a median time to BM diagnosis of 3.7 yrs, while 3 (10%) presented with de novo brain-only metastatic disease. Primary breast tumors were Her-2+ in 15 (50.0%), triple negative in 10 (33.3%), and ER+ in 5 (16.7%) patients. Twenty-eight (93.3%) patients were symptomatic with headache being the most common presentation (46.7%). The median number of BM at BM diagnosis was 2 (range, 1–41), and the median total lesion volume was 15.1 cc (range, 0.39–99.35 cc). Of the 25 (83.3%) patients who underwent neurosurgical resection (NSR), pathology of the BM was Her-2+ in 12 (48%), triple negative in 9 (36%), and ER/PR+ in 4 (16%). Five (20%) patients exhibited receptor discordance between primary and BM, including 3 with ER/PR discordance and no HER2 discordance. All patients received radiation therapy, including 86.7% stereotactic radiosurgery (median dose: 24 Gy in 3 fractions) and 13.3% whole-brain radiotherapy (median dose: 30 Gy in 10 fractions). Eighteen (60.0%) patients started new systemic therapy at BM diagnosis. Median follow-up after BM diagnosis was 26.5 months. The 1- and 2-year OS rates were 97% (95% CI: 78%-100%) and 84% (95% CI: 62%-94%), respectively. Patients who started new systemic therapy post-BM diagnosis had a 1-year OS of 94% and a 2-year OS of 87%, while those without therapy change showed 1-year OS of 100% and 2-year OS of 80% (p=0.53). Median intracranial PFS was 14.6 mo. LMD PFS was 28.3 mo with 16.7% developing LMD. Only 10% of patients developed extracranial metastases with extracranial PFS of 54.3 months. Brain-only metastatic breast cancer patients appear to be a distinct patient population with younger age and longer survival than metastatic breast cancer patients with BM. Further research evaluating treatment paradigms for this patient population is warranted. Tugce Kutuk (she/her/hers), MD (Presenting Author) - The Ohio State University; Marshall Harrell, MD (Co-Author) - The Ohio State University; Rituraj Upadhyay, MD (Co-Author) - The Ohio State University; Yevgeniya Gokun, MS (Co-Author) - The Ohio State University; Mariella A. Mestres-Villanueva, MS (Co-Author) - The Ohio State University; Sierra J. Daniel, MHA (Co-Author) - The Ohio State University; Sachin Jhawar, MD (Co-Author) - The Ohio State University; John C. Grecula, MD (Co-Author) - The Ohio State University; Raju Raval (he/him/his), MD, DPhil (Co-Author) - The Ohio State University; Evan Thomas (he/him/his), MD, PhD (Co-Author) - The Ohio State University; Raj Singh, MD (Co-Author) - Department of Radiation Oncology, The James Cancer Hospital and Solove Research Institute at The Ohio State University Wexner Medical Center; Simeng Zhu, MD (Co-Author) - The Ohio State University; Dukagjin Blakaj (he/him/his), MD, PhD (Co-Author) - The Ohio State University; Arnab Chakravarti (he/him/his), MD (Co-Author) - The Ohio State University; Joshua D.. Palmer, MD (Co-Author) - Department of Radiation Oncology, The James Cancer Hospital and Solove Research Institute at The Ohio State University Wexner Medical Center; Sasha Beyer (she/her/hers), MD, PhD (Co-Author) - The Ohio State University