Outcomes and prognostic factors in breast cancer patients with leptomeningeal metastasis: Insights from a retrospective analysis.

e14002 Background: Leptomeningeal metastasis (LM) is a rare and aggressive complication of breast cancer (CA) associated with poor survival. This study aims to evaluate patient characteristics, treatment effectiveness, and survival outcomes in patients with breast CA and LM by analyzing retrospective patient data. Methods: We analyzed the Rochester Regional Health System patient registry, encompassing two tertiary care hospitals and three cancer centers in Rochester, NY, from January 2011 to September 2024 using grouped ICD-10 and SNOMED codes for breast cancer, central nervous system metastasis, and leptomeningeal metastasis. Initial search yielded 76 patients. We included any patient with breast CA and LM and excluded the rest resulting in a cohort of 10 patients. We collected data on age, tumor subtype, ECOG status, and treatment. Overall survival (OS) was calculated using descriptive statistics. Results: Among the 10 patients, median age was 56 years (range: 29-67) at breast CA diagnosis and 59 years (range: 50-69) at LM diagnosis. The most prevalent subtype was ER/PR+ invasive ductal CA (50%). Median time from breast CA diagnosis to LM diagnosis was 48 months (mo) (range: 3-260). 90% of patients had extracranial (bone, liver, lungs, and uterus) metastases before LM with a median time of 23.2 mo (range: 0-98) from metastatic CA to LM. Brain MRI revealed diffuse LM in 70% and CSF cytology was positive in 20% of patients. Treatment(s) included mastectomy (90%), radiotherapy (80%), ≥1 line of therapy (90%), and ≥3 lines of therapy (30%). Details of therapy included hormonal therapy (70%), chemotherapy (60%), palbociclib (30%), intrathecal methotrexate (10%), atezolizumab (10%), sacituzumab-govitecan (10%) and alpelesib (10%). At data cut-off time, all patients had died with 60% of deaths due to intracranial disease progression. Median OS was 70 mo (range: 3-252) from breast CA diagnosis and 30 days (range:2-635) from LM diagnosis. Invasive lobular CA was associated with shorter median OS post-LM (OS-LM) vs invasive ductal CA (1.7 vs 4.16 mo, p = 0.2). Triple-negative breast CA (TNBCA) was associated with shorter OS-LM vs other receptor (ER/PR/HER 2) status (0.5 vs 5.9 mo, p = 0.3). Patient ECOG-3 was associated with shorter OS-LM vs ECOG status 0, 1, or 2 (2 vs 4.42 mo, p = 0.8). Radiation therapy for breast CA was associated with longer OS-LM vs no radiation therapy (5.2 mo vs 0.67 mo, p = 0.07). Multimodal therapy (≥3 modalities) was associated with a longer OS-LM vs ≤2 treatment modalities (4.67 vs 1.2 mo, p = 0.4). The impact of individual therapies could not be assessed due to limited sample size. Conclusions: LM in breast CA represents a rare but highly aggressive condition with poor OS. Invasive lobular CA and TNBCA were associated with shorter survival post-LM. Multimodal treatment showed statistically nonsignificant improved survival providing a benchmark for future studies.