BSLD-08 MAL2 AS A POTENTIAL DRIVER AND PROGNOSTIC MARKER OF LEPTOMENINGEAL COLONIZATION IN LUNG AND BREAST CANCER
Yi Zhang, Morgan Sokol, Sophia Chernikova, Minkyung Kang, Melanie Hayden GephartAbstract
Background
Leptomeningeal disease (LMD) is a devastating manifestation of systemic malignancy characterized by the colonization of the subarachnoid space. Tissue availability limits study of the molecular mechanisms that allow tumor cells to adapt to this unique niche. We investigated the role of MAL2, a protein involved in membrane trafficking and transcytosis, as a mediator of LMD pathogenesis.
Methods
We performed whole-transcriptome sequencing (CSF-Seq) on cell-free RNA from the CSF of patients with lung LMD (n = 15), breast LMD (n = 15), and non-cancer controls (n = 7). Findings were validated using single-cell RNA sequencing data of circulating tumor cells (CTCs) from a publicly available dataset (n = 5). High-resolution spatial transcriptomics (Xenium, 10x Genomics) and immunofluorescence were used to characterize MAL2 localization within an LMD rapid autopsy specimen. Protein-level validation was conducted via Western blot analysis comparing brain-tropic breast cancer cell sublines to parental lines (MDA-MB-231 and MCF-7).
Results
MAL2 was consistently and significantly upregulated in the CSF of both lung and breast LMD patients compared to non-cancer controls. High MAL2 expression was associated with a clinically meaningful reduction in survival, with median survival of 2.17 months compared to 8.44 months in the low-expression group (p = 0.14). scRNA-seq of CTCs and Xenium spatial analysis confirmed that MAL2 expression is restricted to metastatic tumor cells, specifically co-localizing with epithelial markers like EPCAM, rather than the immune or stromal microenvironment. Western blot analysis revealed enriched MAL2 protein levels in brain-tropic cell lines, suggesting a functional role in CNS-specific metastasis.
Conclusion
Our findings identify MAL2 as a novel marker of LMD that correlates with poor clinical outcomes. The tumor-specific expression of MAL2 and its enrichment in brain-tropic models suggest it may represent a critical adaptation for the subarachnoid space, potentially serving as a prognostic biomarker and a target for disrupting leptomeningeal colonization.