Arsenal Medical agreed on Tuesday to sell itself to Terumo Neuro. NeoCast, the product Terumo wants, is investigational and can't be sold in the United States. The trial meant to win its approval started in August and isn't scheduled to finish collecting its primary data until January 2028. Terumo is buying more than a year ahead of that data. The trial it is buying into only has to match a product Medtronic already proved.
NeoCast is a liquid that a physician injects through a catheter to block the middle meningeal artery. That artery is believed to feed chronic subdural hematoma, a collection of blood on the surface of the brain that mostly affects older patients. The usual treatment is surgery to drain the blood, and the hematoma can come back afterward.
Medtronic proved the procedure
Medtronic sponsored a randomized trial, EMBOLISE, in which some patients had surgery alone and others had surgery plus embolization with Onyx, Medtronic's own liquid embolic. Adding Onyx cut the rate of recurrence or reoperation by roughly 63%, NeuroNews International reported. The results ran in the New England Journal of Medicine in November 2024, and thirteen months later Onyx became the first product in the United States indicated for the procedure.
What Arsenal's trial has to show
Five months after that, in May 2026, the FDA approved Arsenal's pivotal trial, RADIANT. It will randomize about 360 patients two to one between NeoCast and Onyx, at up to 35 sites in the United States and Australia. The ClinicalTrials.gov listing calls the primary comparison non-inferiority: at 90 days, NeoCast patients have to do no worse than Onyx patients on a combined count of treatment failures, meaning hematoma that remains or returns, reoperation, or a major adverse event.
Medtronic had no such comparator. Until December 2025 no embolic was approved for this use, so EMBOLISE had to beat surgery alone. RADIANT compares one embolic with another and takes the procedure's benefit as settled.
Arsenal's pitch for NeoCast over Onyx is the formulation, which contains no solvent and no adhesive. CEO Upma Sharma has said many physicians still rely on older embolics that can be difficult to use and contain one or the other. NeoCast is designed to be delivered without pain, and in Arsenal's first-in-human study in hematoma, 10 of the 24 patients were treated without general anesthesia. The hematoma resolved completely in 18.
What Terumo is buying
Terms weren't disclosed. What Arsenal brings is NeoCast itself, a pivotal trial with FDA approval and its first patients enrolled, and two small first-in-human studies. One is the 24-patient hematoma study. The other used NeoCast to cut off blood supply to brain tumors before surgery. Of those two uses, the one that reached a pivotal trial and a buyer is the one where another company had already proved the therapy.
Whatever Terumo paid, the open question it bought is whether NeoCast performs about as well as Onyx in 360 patients, and the human evidence so far in this use is one 24-patient feasibility study. Medtronic's open question was whether the procedure worked at all.
Going first
Going first cost Medtronic a trial and bought it a head start: Onyx has been on label since December 2025, and NeoCast's primary data isn't due until 2028. I've been the one going first. Galen Robotics' De Novo created a new regulation, and any later company can cite our device as its predicate. We kept the ability to clear our next feature against our own device. The next company gets to skip the argument we had to make.
Dave's take
When I weigh a first indication now, I start with who has already proved the therapy and whether the FDA will accept a comparison against their product. I'd still want to read Arsenal's terms before calling this a good exit for the people who built the material, because how much of the payment waits on the 2028 data isn't public.
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Dave Saunders is the founder of Base Reality Group and a Fractional CPO for product companies. He was a founder and operator at Galen Robotics, where the surgical-robotics platform earned FDA De Novo authorization in 2023, and he managed a 35-patent portfolio licensed from Johns Hopkins. He wrote Founders Who Finish and publishes The Build. More about Dave →