New Diagnostic Test Gains Traction, Expanding Access for Brain Metastasis Patients

NEW YORK, NY – November 20, 2025

A Critical Need Addressed

Patients battling brain metastasis, a devastating complication of many cancers, are gaining access to a more precise diagnostic tool thanks to a national coverage agreement between Plus Therapeutics Inc. and Humana. The agreement, effective October 29, 2025, expands access to CNSide®, a cerebrospinal fluid (CSF) assay designed to detect and monitor metastatic cancer in the central nervous system. This crucial step follows a similar national coverage decision by UnitedHealthcare, now bringing the total potential reach of CNSide® to over 67 million lives.

For years, diagnosing leptomeningeal metastasis (LM), cancer that has spread to the fluid surrounding the brain and spinal cord, has been a significant challenge. Traditional methods, relying on CSF cytology and MRI, often lack the sensitivity to detect the disease early, leading to delayed diagnoses and poorer outcomes. “The current standard of care simply isn’t sufficient for many patients,” says one oncologist, speaking anonymously. “We frequently see false negatives, which means the cancer isn't detected until it’s progressed further.” The median survival for patients with leptomeningeal disease remains low, typically ranging from 2-6 months, underscoring the urgent need for more sensitive and accurate diagnostic tools.

The Promise of CNSide®

CNSide® offers a significant leap forward in diagnostic accuracy. The assay utilizes a microfluidic platform to enumerate tumor cells in CSF, providing a quantitative assessment of disease burden. Beyond simply detecting the presence of cancer cells, CNSide® also offers molecular characterization, identifying genetic mutations that can inform treatment decisions. This precision medicine approach allows oncologists to tailor therapies to the specific characteristics of each patient's cancer. “The ability to identify actionable mutations is a game-changer,” explains a medical researcher familiar with the technology. “It allows us to select the most effective therapies and avoid treatments that are unlikely to work.”

Clinical trials have demonstrated the superior performance of CNSide® compared to traditional methods. The FORESEE study, a prospective clinical trial, showed that CNSide® influenced clinical management decisions in over 90% of LM cases, significantly surpassing a pre-established target. Furthermore, the assay demonstrated 2.8 times higher diagnostic sensitivity compared to standard CSF cytology. The improved accuracy and ability to guide treatment decisions have led to growing acceptance of CNSide® within the medical community and, crucially, amongst major payers like Humana and UnitedHealthcare.

Humana's Strategic Investment & Broader Implications

Humana’s decision to cover CNSide® nationally is a clear indication of the growing recognition of the value of advanced diagnostics in cancer care. The payer’s investment signals a shift towards a more proactive and personalized approach to disease management. While specific details regarding Humana’s rationale haven’t been publicly released, industry analysts suggest the company recognizes the potential of CNSide® to improve patient outcomes and potentially reduce overall healthcare costs in the long run. Early and accurate diagnosis, coupled with targeted therapies, can prevent unnecessary interventions and optimize treatment plans.

The expansion of coverage also validates Plus Therapeutics’ commercial strategy, which focuses on securing favorable reimbursement rates and building a robust market access framework. The company estimates a total addressable market of $6 billion in the U.S. for CNSide®, and the expanded coverage agreements are crucial steps towards tapping into this significant opportunity. “This isn’t just about a single test; it’s about a paradigm shift in how we diagnose and treat brain metastasis,” states one healthcare industry consultant. “Payers are increasingly recognizing the value of investing in innovative technologies that can improve patient care and deliver measurable results.”

Looking Ahead: The Future of CNS Diagnostics

While CNSide® represents a significant advancement in CNS diagnostics, the field is rapidly evolving. Researchers are exploring other liquid biopsy techniques, including the analysis of circulating tumor DNA (ctDNA) in CSF, to further improve diagnostic accuracy and identify new therapeutic targets. The development of more sensitive and specific assays will be crucial for enabling earlier detection, personalized treatment, and ultimately, improving outcomes for patients with brain metastasis. Plus Therapeutics is actively expanding its commercial footprint, initially launching in Texas and planning rapid expansion into additional states. The company anticipates meaningful revenue contributions from CNSide Diagnostics beginning in fiscal year 2026. This agreement with Humana, following the previous one with UnitedHealthcare, solidifies the company’s position as a leader in the rapidly evolving field of CNS diagnostics and personalized cancer care.