Background Due to recent concerns about the toxicity of trastuzumab emtansine (T-DM1) with stereotactic radiation, we assessed our institutional outcomes treating HER2-positive breast cancer brain metastases (BCBM) with T-DM1 and stereotactic radiation. Methods This is a single institution series of 16 patients with HER2-positive breast cancer who underwent 18 stereotactic sessions to 40 BCBM from 2013 to 2019 with T-DM1 delivered within 6 months. The Kaplan-Meier method was used to calculate overall survival (OS), local control (LC), distant intracranial control (DIC), and systemic progression-free survival (sPFS) from the date of SRS. A neuro-radiologist independently reviewed follow-up imaging. Results One patient had invasive lobular carcinoma, and 15 patients had invasive ductal carcinoma. All cases were HER2-positive, while 10 were hormone receptor (HR) positive. Twenty-four lesions were treated with stereotactic radiosurgery (SRS) to a median dose of 21 Gy (14–24 Gy). Sixteen lesions were treated with fractionated stereotactic radiation (FSRT) with a median dose of 25 Gy (20-30Gy) delivered in 3 to 5 fractions. Stereotactic radiation was delivered concurrently with T-DM1 in 19 lesions (48%). Median follow up time was 13.2 months from stereotactic radiation. The 1-year LC, DIC, sPFS, and OS were 75, 50, 30, and 67%, respectively. There was 1 case of leptomeningeal progression and 1 case (3%) of symptomatic radionecrosis. Conclusions We demonstrate that stereotactic radiation and T-DM1 is well-tolerated and effective for patients with HER2-positive BCBM. An increased risk for symptomatic radiation necrosis was not noted in our series.

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Background: Advances in imaging and systemic therapy have improved the survival for patients with breast cancer brain metastases (BCBM). However, an improved understanding of patients with long-term survival after stereotactic radiation (SRT) for BCBM is warranted and could allow for better prognostication and personalized treatment. Methods: This is a single institution retrospective review of 188 patients who underwent SRT sessions to 685 BCBM from August 2004 to June 2020. Patients who were lost to follow up within 2 years after SRT were excluded. Patients were stratified into 2 groups: those with overall survival (OS) from SRT less than 2 years (short-term survival, STS) and those with OS from SRT of at least 2 years (long-term survival, LTS). Patient, tumor, and treatment characteristics were compared between the 2 groups via the student t-test and Chi-square testing as appropriate. The Kaplan-Meier (KM) method was used to calculate OS, local control (LC), and distant intracranial control (DIC) from the date of SRT. The reverse KM method was used to estimate follow-up from SRT. Results: The median follow up from BCBM diagnosis was 52.8 months (95% CI: 40.5-75.2 months). Of the 685 treated BCBMs, 552 (81%) received stereotactic radiosurgery (SRS) to a median dose of 21 Gy (12-24 Gy) and 133 received fractionated stereotactic radiation therapy (FSRT) to a median dose of 25 Gy (20-35 Gy) in 3-5 fractions. The 2-year LC, DIC, and OS was 78.4%, 26.5%, and 38.3%, respectively. The 5-year OS was 19%. There were 72 patients (38%) in the LTS group and 116 patients (62%) in the STS group. The LTS group had lower rates of invasive lobular carcinoma (0% vs 6%, p=0.001) and higher rate of HER2+ disease (61% vs 30%, p< 0.001). The LTS group had lower rates of concurrent extracranial metastasis (74% vs 89%, p=0.008) and lung metastasis (33% vs 53%, p=0.009), though there were no differences in the rates of bone or liver metastasis. The LTS group had less BCBM at the time of SRT (mean 1.9 vs 2.5, p=0.013) and more often received SRT to a single BCBM (65% vs 42%, p=0.002). There were no significant differences in age or performance status between the groups. Conclusion: Prognosis for patients with BCBM is heterogeneous, as a minority of patients have prolonged OS after SRT. These patients more often have limited BCBM, HER2+ disease, and a lower extracranial disease burden. Citation Format: Joseph D. Tang, Matthew N. Mills, Chetna Thawani, Daniel E. Oliver, Aixa Soyano, Arnold Etame, Hsiang-Hsuan Michael Yu, Nam Tran, Michael A. Vogelbaum, Peter A. Forsyth, Brian J. Czerniecki, Hatem H. Soliman, Hyo S. Han, Kamran A. Ahmed. Characteristics of Long-Term Survival in Breast Cancer Brain Metastasis after Stereotactic Radiation [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr PD7-06.