A single center retrospective cohort study of patients with metastatic breast cancer and leptomeningeal disease: Updated survival data and subgroup analyses by breast cancer subtype.

Abstract

1108 Background: Patients (pts) with metastatic breast cancer (MBC) and leptomeningeal disease (LMD) have a poor prognosis with limited therapies. We previously reported data from our retrospective LMD registry; here we provide an update with additional pts and subgroup analyses highlighting differences in treatment and survival by breast cancer subtype. Methods: In this single center retrospective cohort study, we identified pts with MBC and LMD who received care from 2000-2024 and abstracted key clinical, treatment, and overall survival (OS) data. Results: We identified 111 pts with MBC and LMD, including pts with the following subtypes: HR+/HER2- (n=53, 47.7%), HER2+ (n=30, 27.0%), and triple negative breast cancer (TNBC; n=28, 25.2%). The majority of pts had concurrent brain metastasis (n=82, 73.9%). Median time from diagnosis of MBC to LMD was 16.4 months (mo) (range 0-101.3 mo). Pts received a median of 3 lines of therapy prior to the diagnosis of LMD (range 0-10) and 1 line after the diagnosis of LMD (range 0-4). Most pts received central nervous system-directed (CNS)-directed therapy (n=94, 84.7%), including intrathecal (IT) therapy (n=42, 37.8%) and/or CNS radiation (n=70, 63.1%). Median OS from the diagnosis of LMD to death was 4.1 mo (range 0.1-78.1 mo) and varied by subtype, with pts with HR+/HER2- or HER2+ MBC and LMD living longer than those with TNBC and LMD (4.2 and 6.8 mo respectively vs. 2.0 mo, p<0.01, HR 2.15, 95% CI 1.36-3.39). There was no difference in OS by histology ductal vs. lobular or by presence or absence of concurrent parenchymal brain metastases. Pts who received IT therapy survived longer than those who did not (7.1 vs. 2.7 mo, p=0.01, HR 0.60, 95% CI 0.40-0.90). There was difference in OS by receipt of CNS-directed radiation therapy. Pts diagnosed with LMD from 2015-2024 lived longer than those diagnosed from 2000-2014 (6.4 vs. 2.9 mo, p=0.04, HR 0.67, 95% CI 0.46-0.99). On multivariable analysis, having TNBC was associated with shorter OS from time of LMD to death (p=0.004, HR 2.03, 95% CI 1.25-3.30). Conclusions: This study represents one of the largest case series of pts with MBC and LMD, including the most pts diagnosed after 2015 to our knowledge. Pts with lobular histology, HER2+ BC, TNBC, and those with de novo MBC were over-represented compared to the general MBC population. Pts with HR+/HER2- or HER2+ disease, LMD diagnosed after 2015, and those who received IT therapy survived longer than their respective cohorts. Novel diagnostic and therapeutic strategies for pts with MBC and LMD remains an area of unmet clinical need.