On August 14, 2025 Plus Therapeutics, Inc. (Nasdaq: PSTV) ("Plus" or the "Company"), a clinical-stage pharmaceutical company developing targeted radiotherapeutics with advanced platform technologies for central nervous system (CNS) cancers, reported positive data from a retrospective analysis of the CNSide Cerebrospinal Fluid (CSF) Assay Platform at the 2025 Society for Neuro-Oncology (SNO)/American Society of Clinical Oncology (ASCO) (Free ASCO Whitepaper) CNS Metastases Conference in Baltimore, Maryland (Press release, Plus Therapeutics, AUG 14, 2025, View Source [SID1234655320]).

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The presentation, titled "The Oncogenic Flip in Patients with Leptomeningeal Metastatic Disease (LMD): Longitudinal Detection in Cerebrospinal Fluid Tumor Cells (CSF-TCs) Reveals Implications for Differential Treatment of the LMD Tumor," was a retrospective, multi-center analysis of 613 CNSide assays ordered by 19 physicians from 5 institutions at 2 health systems for 218 individual patients. 74% of the patients were female and the cancers most analyzed were breast (n=105) and lung (n=65). The research was presented by Priya U. Kumthekar, M.D., Professor of Neurology and Medicine at Northwestern University.

Data Demonstrated:

CSF tumor cells detected in 67% (412/613) patients using CNSide;
66 patients underwent 2 or more CSF draws; 24 patients underwent 5 or more;
20% (13/66) of patients were found to have a flip in immunocytochemistry (ICC) detection; and
88% (58/66) of patients were found to have a flip in FISH probe detection.
"The CNSide CSF Assay Platform can be used to detect gene amplification on CSF tumor cells of patients with LM and, therefore, may provide therapeutic insights to specifically target the LM tumor," said Priya U. Kumthekar, M.D., "Further, longitudinal CSF tumor cell analysis using CNSide may provide insights to modify treatment of the LM tumor over time."

The data builds upon previously announced results, "CSF Tumor Cell (CSF-TC) Detection, Quantification and Biomarker Assessment Helps in Clinical Management of Breast Cancer and Non-Small Cell Lung Cancer Patients Having Leptomeningeal Disease," from the prospective FORESEE study, which was also presented by Dr. Kumthekar, principal investigator. The study met key primary and secondary endpoints and showed that the CNSide CSF Assay platform influenced clinical management decisions in over 90% of LM cases. Further the CNSide CSF Assay demonstrated 2.8 times the diagnostic sensitivity versus standard CSF cytology.

About CNSide Diagnostic, LLC
CNSide Diagnostics, LLC is a wholly owned subsidiary of Plus Therapeutics, Inc. that develops and commercializes proprietary laboratory-developed tests, such as CNSide, designed to identify tumor cells that have metastasized to the central nervous system in patients with carcinomas and melanomas. The CNSide CSF Assay Platform enables quantitative analysis and molecular characterization of tumor cells and circulating tumor DNA in the cerebrospinal fluid that inform and improve the management of patients with leptomeningeal metastases.

About Leptomeningeal Metastases
Leptomeningeal metastases (LM) are a rare but severe complication of advanced cancer, affecting the fluid-lined structures of the central nervous system. LM occurs in approximately 5% of patients with metastatic cancer, but the actual incidence may be higher as it can be difficult to diagnose. Postmortem studies show the frequency of LM to be around 20% or more, highlighting healthcare providers’ need for more sensitive diagnostic options.