Radiotherapeutics For CNS Cancers With Plus Therapeutics' Marc Hedrick, M.D.

What It Covers

Marc Hedrick, CEO of Plus Therapeutics, details the development of Rhenium-186 radiotherapeutic Rayovik for CNS cancers including glioblastoma and leptomeningeal disease, explains the company's diagnostic subsidiary See Inside, and outlines why targeted radiotherapy delivers over 10 times the radiation dose of external beam treatment.

Key Questions Answered

• •Therapeutic index advantage: Rayovik achieves a 100-to-1 therapeutic index in CNS cancers compared to roughly 2-to-4-to-1 for alpha emitter competitors. This allows single-dose delivery of up to 740 gray versus the 30-50 gray maximum from fractionated external beam radiation, with no identified upper dose limit in two separate phase one trials.
• •Leptomeningeal disease scale: Approximately 125,000 US patients annually develop leptomeningeal metastases, roughly ten times the 15,000 annual glioblastoma cases, and the condition is likely two-to-four times underdiagnosed. Median survival with current treatment is two-to-four months, making it the higher commercial priority over glioblastoma despite glioblastoma entering trials earlier.
• •Diagnostic gap as business opportunity: Standard-of-care cytology for leptomeningeal cancer dates to 1904 and detects disease only 40% of the time. See Inside's tumor cell enumeration assay detects a single cell in five cubic centimeters of cerebrospinal fluid, has 70 million US lives covered for reimbursement, and represents an estimated $6 billion gap in the global diagnostic market.
• •Supply chain scalability via Rhenium-186: Rhenium-186's 90-hour half-life enables centralized US manufacturing at Missouri's MURR reactor, overnight shipping to hospitals, and two-to-four days of usable shelf life on arrival. The drug bypasses the radiopharmacy entirely, ships through standard radiology receiving, and allows dose recalculation if a patient misses a scheduled injection window.
• •Surrogate endpoint strategy for approval: Because no approved drugs or established clinical trial models exist for leptomeningeal cancer, Plus Therapeutics secured FDA alignment in a January 2026 Type B meeting around compartmental endpoints beyond overall survival and the potential use of See Inside tumor cell counts as a validated surrogate endpoint, accelerating the path toward a pivotal trial.