Plus Therapeutics to Present Positive FORESEE Clinical Trial Summary Demonstrating Utility of CNSide™ Cerebrospinal Fluid Assay in Diagnosis and Clinical Management of Patients with Leptomeningeal Metastases

Prospective FORESEE trial of CNSide Cerebrospinal Fluid (CSF) Assay met key primary and secondary endpoints

CNSide CSF Assay influenced clinical management decisions in over 90% of leptomeningeal metastases (LM) cases

Assay demonstrated 2.8 times the diagnostic sensitivity vs. standard cytology

AUSTIN, Texas, Nov. 22, 2024 (GLOBE NEWSWIRE) — CNSide Diagnostics, LLC, a wholly owned subsidiary of Plus Therapeutics, Inc. (Nasdaq: PSTV) (“Plus” or the “Company”), will present data from the FORESEE trial showcasing the CNSide CSF Assay Platform’s utility in diagnosing and guiding clinical decision making for breast cancer and non-small cell lung cancer patients with LM. The data will be presented at the 2024 Society for Neuro-Oncology (SNO) Annual Meeting November 21-24 in Houston, Texas.  

“Current gold standard CSF cytology lacks the sensitivity needed to reliably diagnose LM in most clinical situations and lacks utility for disease monitoring,” said Marc H. Hedrick, M.D., Plus Therapeutics’ President and Chief Executive Officer. “The FORESEE trial shows that CNSide may be a useful tool in accurately identifying all patients with LM, ruling out patients at risk, and enhancing the disease management and monitoring of LM.”

Key highlights:

• The FORESEE trial achieved its primary endpoint, demonstrating that CNSide influenced treatment decisions in over 90% of cases evaluated, surpassing the predetermined 20% primary endpoint target
• CNSide demonstrated enhanced sensitivity in detecting tumor cells (80%) vs. CSF cytology (29%) in patients with LM
• CNSide identified actionable mutations in the CSF, such as HER2 amplification, influencing 24% of therapeutic selection decisions
• CNSide exhibited high specificity, with no tumor cells detected in patients without LM
• CNSide demonstrated improved Negative Predictive Value in ruling out LM (25%) vs. CSF cytology (10%)
• CNSide revealed HER2 positivity in LM tumors in 60% of breast cancer patients with HER2-negative primary tumors, informing physician treatment strategies

The data will be presented on Sunday, November 24, at 10:15 a.m. CST in a session titled, “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 (FORESEE Study, NCT-5414123),” by Priya Kumthekar, M.D., Associate Professor of Neurology and Hematology/Oncology, and Director of Brain Metastases Program at Northwestern, University, Chicago, Illinois.

About CNSide Diagnostic, LLC
CNSide Diagnostics, LLC is a wholly owned subsidiary of Plus Therapeutics, Inc. that develops and commercializes proprietary clinical diagnostic laboratory assays, such as CNSid, designed to identify tumor cells that have metastasized to the central nervous system in patients with carcinomas and melanomas. The CNSid Assay Platform enables quantitative analysis and molecular characterization of tumor cells and circulating tumor DNA in the cerebrospinal fluid that inform and improve the clinical management of patients with leptomeningeal metastases. The Company is planning to commercialize CNSide in the U.S. in 2025.

About CNSide Test
The CNSide Cerebrospinal Fluid (CSF) Assay Platform consists of four laboratory developed tests (LDTs) used for diagnosis, treatment selection, and treatment monitoring of patients with Leptomeningeal Metastases (LM) from carcinomas or melanoma. The CNSide platform facilitates tumor cell detection / enumeration and biomarker identification using cellular assays (immunocytochemistry (ICC) and fluorescence in situ hybridization (FISH)) and molecular assays (next generation sequencing (NGS)). The CNSide CSF tumor cell enumeration LDT is currently being used in the ReSPECT-LM trial as an exploratory endpoint, and is anticipated to become commercially available in 2025.

About Leptomeningeal Metastases (LM)

LM is a rare complication of cancer in which the primary cancer spreads to the cerebrospinal fluid (CSF) and leptomeninges surrounding the brain and spinal cord. All malignancies originating from solid tumors, primary brain tumors, or hematological malignancies have this LM complication potential with breast cancer as the most common cancer linked to LM, with 3-5% of breast cancer patients developing LM. Additionally, lung cancer, GI cancers and melanoma can also spread to the CSF and result in LM. LM occurs in approximately 5% of people with cancer and is usually terminal with 1-year and 2-year survival of just 7% and 3%, respectively. The incidence of LM is on the rise, partly because cancer patients are living longer and partly because many standard chemotherapies cannot reach sufficient concentrations in the spinal fluid to kill the tumor cells; yet, there are no FDA-approved therapies specifically for LM patients, who often succumb to this complication within weeks to several months, if untreated.

About FORESEE Clinical Trial

The FORESEE Study is a multi-center, prospective clinical trial enrolled patients with Breast or Non-Small Cell Lung Cancer (NSCLC) who have suspicious or confirmed Leptomeningeal Metastases (LM). Standard of Care methods to diagnose or assess the treatment response of LM (Clinical Evaluation, MRI and Cytology) have limited sensitivity and specificity. This creates challenges for physicians to manage LM or determine the best course of treatment. The goal of the FORESEE Study was to evaluate the performance of CNSide in monitoring the LM’s response to treatment and to assess the impact of CNSide on treatment decisions made by physicians.

About Rhenium (¹⁸⁶Re) obisbemeda

Rhenium (¹⁸⁶Re) obisbemeda is a novel injectable radiotherapy specifically formulated to deliver direct targeted high dose radiation in CNS tumors in a safe, effective, and convenient manner to optimize patient outcomes. Rhenium (¹⁸⁶Re) obisbemeda has the potential to reduce off target risks and improve outcomes for CNS cancer patients, versus currently approved therapies, with a more targeted and potent radiation dose. Rhenium-186 is an ideal radioisotope for CNS therapeutic applications due to its short half-life, beta energy for destroying cancerous tissue, and gamma energy for real-time imaging. Rhenium (¹⁸⁶Re) obisbemeda is being evaluated for the treatment of recurrent glioblastoma and leptomeningeal metastases in the ReSPECT-GBM and ReSPECT-LM clinical trials. ReSPECT-GBM is supported by an award from the National Cancer Institute (NCI), part of the U.S. National Institutes of Health (NIH), and ReSPECT-LM is funded by a three-year $17.6M grant by the Cancer Prevention & Research Institute of Texas (CPRIT).

About Plus Therapeutics
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 for patients. Combining image-guided local beta radiation and targeted drug delivery approaches, the Company is advancing a pipeline of product candidates with lead programs in recurrent glioblastoma (GBM) and leptomeningeal metastases (LM). The Company has built a supply chain through strategic partnerships that enable the development, manufacturing, and future potential commercialization of its products. Plus Therapeutics is led by an experienced and dedicated leadership team and has operations in key cancer clinical development hubs including Austin and San Antonio, Texas. For more information, visit https://plustherapeutics.com/.

Cautionary Statement Regarding Forward-Looking Statements
This presentation 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 “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 following: the uses and benefits of the CNSide CSF Assay Platform, and predicted timeline for commercialization of the CNSide CSF tumor cell enumeration test.

The forward-looking statements included in this press release could differ materially from those expressed or implied by these forward-looking statements because of risks, uncertainties, and other factors that include, but are not limited to, the following: the early stage of the Company’s product candidates and therapies; the results of the Company’s research and development activities, including uncertainties relating to the clinical trials of its product candidates and therapies; the Company’s liquidity and capital resources and its ability to raise additional cash to fund its operations in the near term and long term, on terms acceptable to us or at all; the outcome of the Company’s partnering/licensing efforts; risks associated with laws or regulatory requirements applicable to the Company, including the ability to come into compliance with The Nasdaq Capital Market listing requirements; market conditions; product performance; litigation or potential litigation; competition within the cancer diagnostics and therapeutics field; ability to develop and protect proprietary intellectual property or obtain licenses to intellectual property developed by others on commercially reasonable and competitive terms; manufacturing and supply chain risks; and material security breach or cybersecurity attack affecting the Company’s operations or property. This list of risks, uncertainties, and other factors is not complete. Plus Therapeutics discusses some of these matters more fully, as well as certain risk factors that could affect Plus Therapeutics’ business, financial condition, results of operations, and prospects, in its reports filed with the SEC, including Plus Therapeutics’ annual report on Form 10-K for the fiscal year ended December 31, 2023, quarterly reports on Form 10-Q, and current reports on Form 8-K. These filings are available for review through the SEC’s website at www.sec.gov. Any or all forward-looking statements Plus Therapeutics makes may turn out to be wrong and can be affected by inaccurate assumptions Plus Therapeutics might make or by known or unknown risks, uncertainties, and other factors, including those identified in this press release. Accordingly, you should not place undue reliance on the forward-looking statements made in this press release, which speak only as of its date. The Company assumes no responsibility to update or revise any forward-looking statements to reflect events, trends or circumstances after the date they are made unless the Company has an obligation under U.S. federal securities laws to do so.

Investor Contact
Charles Y. Huang, MBA
Director of Capital Markets and Investor Relations
Office: (202)-209-5751 | Direct (301)-728-7222
chuang@plustherapeutics.com