Plus Therapeutics Presents Positive CNSide CSF Assay Platform Results at the 2025 SNO/ASCO CNS Metastases Conference

CNSide® can quantify leptomeningeal metastases (LM) over time and monitor changes in the expression of multiple targetable mutations

CNSide® may catalyze LM treatment initiation, allow physicians to adapt treatment with real time shifts in tumor biology, and enable personalized cancer therapy

HOUSTON, Aug. 14, 2025 (GLOBE NEWSWIRE) -- 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, today announced 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) CNS Metastases Conference in Baltimore, Maryland.

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.

About Plus Therapeutics

Headquartered in Houston, Texas, Plus Therapeutics, Inc. is a clinical-stage pharmaceutical company developing targeted radiotherapeutics for difficult-to-treat cancers of the central nervous system with the potential to enhance clinical outcomes. Combining image-guided local beta radiation and targeted drug delivery approaches, the Company is advancing a pipeline of product candidates with lead programs in leptomeningeal metastases (LM) and recurrent glioblastoma (GBM). The Company has built a supply chain through strategic partnerships that enable the development, manufacturing, and future potential commercialization of its products. For more information, visit https://www.plustherapeutics.com.

Forward-Looking Statements

This press release contains statements that may be deemed "forward-looking statements" within the meaning of U.S. securities laws, including statements regarding clinical trials, expected operations and upcoming developments. All statements in this press release other than statements of historical fact are forward-looking statements. These forward-looking statements may be identified by future verbs, as well as terms such as "expect," "potential," "anticipating," "planning" and similar expressions or the negatives thereof. Such statements are based upon certain assumptions and assessments made by management in light of their experience and their perception of historical trends, current conditions, expected future developments and other factors they believe to be appropriate.

These statements include, without limitation, statements regarding the potential market for the CNSide CSF Assay, the timing in which the CNSide CSF Assay is commercially launched and commercialization is expanded, revenue and corporate profitability expectations including support reimbursements and payments for the CNSide CSF Assay, the development and utility of the CNSide CSF Assay and expectations as to the Company's future performance, including the next steps in developing the Company's product candidates.

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