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

Rhea-AI Summary

Plus Therapeutics (NASDAQ:PSTV) presented positive data from their CNSide® Cerebrospinal Fluid (CSF) Assay Platform at the 2025 SNO/ASCO CNS Metastases Conference. The retrospective analysis, involving 613 CNSide assays from 218 patients across 5 institutions, demonstrated significant capabilities in detecting and monitoring leptomeningeal metastases (LM).

Key findings include 67% detection rate of CSF tumor cells, with notable observations of immunocytochemistry and FISH probe detection changes in patients with multiple CSF draws. The platform showed 2.8 times higher diagnostic sensitivity compared to standard CSF cytology and influenced clinical management decisions in over 90% of LM cases.

Insights

Oncology and Diagnostics Expert

Plus Therapeutics' CNSide assay shows promising ability to detect and monitor leptomeningeal metastases, potentially transforming treatment approaches.

The data presented at the SNO/ASCO CNS Metastases Conference represents a significant advancement in the management of leptomeningeal metastases (LM), a notoriously difficult-to-treat form of cancer spread. The CNSide platform demonstrated 67% detection rate of CSF tumor cells across 613 assays, substantially outperforming standard CSF cytology with 2.8 times greater diagnostic sensitivity.

What's particularly valuable is the platform's ability to monitor changes in tumor biology over time. The study showed that 20% of patients experienced shifts in immunocytochemistry detection and a remarkable 88% showed changes in FISH probe detection across multiple CSF draws. This capability to detect "oncogenic flips" provides clinicians with crucial real-time information about evolving tumor characteristics.

The clinical implications are substantial. The FORESEE study demonstrated that CNSide influenced clinical management decisions in over 90% of LM cases, potentially allowing physicians to adapt treatment strategies as tumor biology changes. For Plus Therapeutics, this strengthens their position in the CNS cancer space by complementing their radiotherapeutic pipeline with advanced diagnostic capabilities.

This technology addresses a critical unmet need in neuro-oncology. LM diagnosis has historically relied on less sensitive methods, often leading to delayed treatment initiation and suboptimal outcomes. By providing both enhanced detection and molecular characterization of CSF tumor cells, CNSide could enable earlier intervention and more personalized treatment approaches for patients with these challenging CNS malignancies.

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.

Investor Contact
CORE IR
investor@plustherapeutics.com 

FAQ

What were the key findings of Plus Therapeutics' (PSTV) CNSide platform study presented at SNO/ASCO 2025?

The study showed 67% detection rate of CSF tumor cells, 2.8x higher diagnostic sensitivity than standard cytology, and influenced clinical decisions in over 90% of LM cases.

How many patients were included in Plus Therapeutics' CNSide platform analysis?

The analysis included 218 patients across 5 institutions, with 613 CNSide assays ordered by 19 physicians from 2 health systems.

What types of cancer were most analyzed in the PSTV CNSide study?

The most analyzed cancers were breast cancer (105 patients) and lung cancer (65 patients), with 74% of the total patients being female.

How does Plus Therapeutics' CNSide platform help in treating leptomeningeal metastases?

CNSide helps by quantifying leptomeningeal metastases over time, monitoring changes in targetable mutations, and enabling physicians to adapt treatment based on real-time shifts in tumor biology.

What was the significance of the 'oncogenic flip' detected by PSTV's CNSide platform?

The study found that 20% of patients showed changes in immunocytochemistry detection and 88% showed changes in FISH probe detection, indicating potential needs for treatment modification over time.