Abstract PS11-02: Clinical risk factors of Central Nervous System (CNS)-related death in patients with HER2-positive metastatic breast cancer

Abstract Background: Central nervous system (CNS) relapse represents a challenge in the management of patients with HER2-positive (+) metastatic breast cancer. Data regarding the impact of brain metastases (BrM) and CNS involvement on mortality are sparse. In this study we sought to determine the proportion of HER2+ MBC patients in which CNS disease is the cause of death and identify risk factors associated with CNS-related mortality. Methods: We reviewed medical records of 294 consecutive patients with HER2+ MBC and diagnosis of CNS disease including parenchymal BrM, leptomeningeal disease (LMD) or dural metastases (DM), treated at Memorial Sloan Kettering Cancer Center between August 2010 and April 2022. HER2-positivity was assessed at the first diagnosis of metastatic disease (any site). Clinicopathologic characteristics including disease burden at presentation, timing of CNS disease and extracranial metastases (ECM), neurologic complications, and local and systemic treatments were collected. CNS-related death was defined as any death caused by BrM or LMD or DM progression or CNS treatment-associated complications. CNS-related death was estimated using cumulative incidence in the competing risks setting (with death due to other causes as a competing event) and overall survival (OS) was estimated using Kaplan Meier methodology. Risk factors associated with CNS-related death were assessed using sub-distribution hazards regression modeling. Treatments given after CNS disease diagnosis were treated as time-varying variables. Tests were two-sided with statistical significance 0.05. Results: After excluding 19 patients (11 for discordant HER2 status, 5 for concomitant second solid tumor, and 3 for missing data), 275 patients were included in these analyses (258 patients with parenchymal BrM +/- LMD, 8 patients with DM only, 2 patients with DM concomitantly with LMD, and 6 patients with LMD only). Overall, 63/275 (23%) presented with CNS as first and only site of metastasis, 210 (76%) patients developed CNS disease synchronously with or following ECM, and 2 had unknown timing. 125/275 (45%) had de novo MBC, and nearly all patients were treated with CNS local therapies (92% ≥1 radiation treatment and 28% underwent ≥1 BrM resection). The median number of lines of systemic therapy after CNS disease diagnosis was 1 (range: 0-14); 105/275 (38%) patients received a HER2 tyrosine kinase inhibitor (lapatinib: 21%, neratinib: 4.4%, and tucatinib: 12%). The median follow-up was 3.6 years for survivors (range: 0.22 years-12 years). 193/275 (70%) patients died, of whom 105 (54%) died of CNS-related cause. The 3-year OS rate was 40% (95% CI=34%-46%), which varied for patients with BrM only at the diagnosis of metastatic disease 56% (95% CI=43%-69% compared to patients with ECM +/- BrM 35% (95% CI=28%-42% (p=0.05). The cumulative incidence of CNS-related death at 3 years was 33% (95% CI=27%-39%). Upon univariable modeling, LMD and CNS radiation treatment (RT) were associated with CNS-related death, and these associations remained statistically significant in a multivariable model LMD: HR=2.49 (95% CI=1.62-3.83), p 0.0001, and RT: HR=2.91 (95% CI=1.27-6.64), p=0.01. Conclusions: Greater than half of patients with HER2+ with CNS involvement suffered of CNS-related death, with greatest risk among patients with LMD. We hypothesize that the association between radiotherapy and CNS-related death may reflect upfront response to systemic cancer-directed treatments of those in patients with DM only or limited CNS disease extension. CNS-only relapse at metastatic presentation portended improved survival than intra- plus extracranial progression, supporting an approach of aggressive local therapy for selected patients. Multimodality approaches using HER2-directed agents effective against parenchymal BrM, LMD along with extracranial metastases, in combination with local CNS-directed therapies need to be optimized. Citation Format: Emanuela Ferraro, Rabih Bou Nassif, Anne Reiner, Samantha Brown, Umberto Tosi, Katherine Panageas, Chau Dang, Andrew D Seidman, Nelson Moss. Clinical risk factors of Central Nervous System (CNS)-related death in patients with HER2-positive metastatic breast cancer abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PS11-02.