Abstract 6472: Response to PARP inhibitors in patients with breast cancer metastatic to the central nervous system

Abstract Background: Central nervous system (CNS) metastasis from breast cancer can be challenging to treat due to the limited blood brain barrier penetration of many systemic therapies. PARP inhibitors (PARPi) block single-strand DNA break repairs and have activity in cancers with homologous recombination repair deficiency; they are FDA approved for patients with metastatic HER2 negative breast cancer with germline BRCA1/2 mutations. While preclinical studies suggest that PARPi have CNS penetration, clinical data is limited. The goal of our study is to describe the clinical benefit of PARPi in patients with breast cancer CNS metastasis. Methods: This retrospective case series was conducted at three academic cancer centers (Johns Hopkins, Dana-Farber, and Duke) and included patients with the following criteria: (1) age≥18 years with a breast cancer diagnosis (any subtype) ; (2) diagnosis of parenchymal brain metastasis or leptomeningeal disease (LMD) ; and (3) received PARPi (olaparib, talazoparib) for CNS metastasis. Clinical and pathologic information were analyzed with descriptive statistics (median, range) and Kruskal-Wallis rank sum tests. Survival analysis was performed using Kaplan-Meier curves with log-rank p-values. Results: Although this analysis includes one center’s experience, we will present a combined dataset (N = 45) at the main conference. 11 patients were identified at Johns Hopkins. 4 (36. 4%) were Black and 6 (54. 5%) were White; 6 (54. 5%) had ER+HER2- disease and 5 (45. 5%) had TNBC at time of brain metastasis; 5 (45. 5%) had BRCA1 mutations, 5 (45. 5%) had a BRCA2 mutations, and 1 patient (9%) had a BARD1 mutation; 7 (63. 6%) had brain metastasis and 4 (36. 4%) had LMD. Median lines of therapy prior to PARPi was 6 1 - 11; 8 patients (72. 7%) had previous CNS radiation (5 SRS and 3 WBRT) and 3 (27. 3%) had previous CNS surgery. On average, patients remained on PARPi for 5 months 0. 5 - 66, and overall survival (OS) time from PARPi to death was 16 months 2 - 66. Time on PARPi was 5 months 2 - 66 for patients with brain metastasis and 3 months 0. 5 - 10 for those with LMD (p=0. 22). Duration of PARPi and OS did not differ significantly between ER+HER2- and TNBC (p=0. 74 and 0. 69, respectively), BRCA 1 and 2 (p=0. 78 and 0. 72, respectively), or brain and LMD metastasis (p=0. 22 and 0. 91, respectively). Black patients had significantly shorter PARPi duration and survival than White patients (PARPi 2 vs. 8 months, p=0. 028 and OS 4 vs 18 months, p=0. 028). Prior CNS radiation was significantly associated with longer PARPi duration and survival (PARPi 5 vs 1 month, p=0. 02 and OS 17 vs. 3 months, p=0. 032). Prior CNS surgery was significantly associated with longer PARPi duration, but not overall survival (PARPi 18 vs 3 months, p=0. 05 and OS 28 vs. 7 months, p=0. 14). Conclusions: PARPi are associated with significant clinical benefit in patients with breast cancer CNS metastasis. Larger data series will help confirm these observations. Citation Format: Seoho Lee, Rani Bansal, Melissa E. Hughes, Amanda E. Van Swearingen, Heather N. Moore, David O. Kamson, Solmaz Sahebjam, Greg Kirkner, Anna Gorfinkel, Sarah Sammons, Nancy U. Lin, Carey Anders, Cesar A. Santa-Maria. Response to PARP inhibitors in patients with breast cancer metastatic to the central nervous system abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 6472.