BSLD-01 PROGNOSTIC SCORING AND HISTOPATHOLOGICAL CHARACTERISTICS OF BREAST CANCER PATIENTS WITH LEPTOMENINGEAL METASTASES: REAL-WORLD EVIDENCE FROM MULTIPLE TERTIARY CARE CENTERS

Abstract Leptomeningeal metastases (LM) are a rare complication of breast cancer (BC) with poor survival. Literature is inconsistent regarding the most common BC subtype linked to LM. This study analyzes Rochester Regional Health System patient registry, covering two tertiary care centers with three affiliated cancer centers in Rochester, NY (ROC-NY) from January 2011 to September 2024 to identify the predominant BC subtype and to validate two prognostic scoring systems: Institut Curie Simplified Prognostic Score and INDEX Score. Using grouped ICD-10 and SNOMED codes for BC and LM, we identified 76 patients. Only those diagnosed with both BC and LM were included, yielding a cohort of 10 patients. Overall survival (OS) was calculated using descriptive statistics. Median age was 56 (range: 29-67) years at BC diagnosis and 59 (range: 50-69) years at LM. Invasive ductal (IDC) was the prevalent BC subtype (50%), followed by invasive lobular (ILC) (20%) and mixed (20%). ER/PR+, HER2- was the most common receptor configuration (70%) vs triple-negative (TNBCA) (20%) and ER/PR+, HER2+ (10%). Median OS from BC was 70 months (mo) (range: 3-252 mo) and 30 days (range: 2-635 days) post-LM (OS-LM). ILC had shorter OS-LM vs IDC (1.7 vs 4.16 mo, p=0.21). TNBCA had shorter OS-LM vs other receptor configurations (0.5 vs 5.9 mo, p=0.3). Institut Curie simplified prognostic score of 1 was associated with OS-LM of 3.76 mo, and 2 with 3.2 mo. INDEX score of 1 was associated with OS-LM of 4.5 mo, and 2 with 4.2 mo. These values aligned with score predictions. Despite limited sample size, our study validates both the Institut Curie and INDEX prognostic scores and highlights that IDC and ER/PR+, HER2- are the most common BC subtypes linked with LM in ROC-NY population, followed by TNBCA, providing a benchmark for future research.