A large trial is now testing whether an experimental Alzheimer’s drug can stop the disease before memory problems start. The study is called PrevenTRON, and the drug is trontinemab, made by the Swiss drugmaker Roche. It is recruiting about 1,600 people aged 55 to 80 around the world who have no memory problems but are at high risk of developing Alzheimer’s1. An NHS trust in Surrey says it is the first site in Europe to offer the drug in the trial, and the third site worldwide2.
What happened
On 5 September, the Guardian reported that the Surrey and Borders Partnership NHS Foundation Trust would start screening the first European participants the following Monday3. The trust is the lead recruitment site in the UK and can take volunteers from anywhere in the country1. Volunteers first get tests to confirm they have no memory problems. They are then offered a blood test for p-tau217, a protein marker linked to later memory decline and Alzheimer’s3.
People with raised p-tau217 who meet the other criteria are randomly assigned to get either trontinemab or a placebo (a dummy treatment). Researchers then follow them to see how quickly any signs of dementia appear3. The drug is given through a drip into a vein1. PrevenTRON is a Phase 3 study, one of the last and largest stages of testing before a medicine might be considered for wider use4.
Roche first presented the trial’s design at the Alzheimer’s Association International Conference in London in July5. Prof Ramin Nilforooshan, a consultant psychiatrist and the trial’s chief investigator, described the change in focus:
“For decades, research has focused on treating Alzheimer’s disease after symptoms appear. PrevenTRON addresses a different question, whether we can act earlier, before symptoms begin.”3
The evidence so far
Trontinemab is an antibody, a lab-made immune protein, that targets amyloid. Amyloid is a sticky protein that builds up between brain cells in Alzheimer’s2. Roche built the drug by combining an older antibody it had tested before, gantenerumab, with a “shuttle” molecule meant to help it cross the blood-brain barrier6. That barrier is a protective layer that keeps toxins and germs out of the brain1. Some anti-amyloid antibodies are estimated to get less than 1% of their dose into the brain. Roche estimates its shuttle can raise that by 50 times or more1.
All of the human data so far come from an earlier, smaller study in people who already had early Alzheimer’s symptoms, not in healthy people. In a July 2025 press release, Roche said 91% of participants in that study had amyloid levels drop below the threshold for a positive brain scan7. In the group given the higher dose, 49 of 54 people fell below that threshold after 28 weeks, and 39 reached what the company called “deep clearance”7. Roche said brain swelling, a known side effect of this drug class, happened in under 5% of participants. It said all cases were mild on scans and most caused no symptoms7. Those results were presented at the same conference in Toronto in 20258.
The UK trial depends on the blood test. Earlier research found people with the highest p-tau217 levels had an estimated 78% chance of developing memory and thinking problems within 10 years. Separate research found p-tau217 blood tests could identify Alzheimer’s with up to 95% accuracy3.
What it does not show yet
There are no results from PrevenTRON. Clearing plaque on a brain scan is a lab measure. It is not the same as showing that people keep their memory or avoid dementia. Nilforooshan stressed this in an interview with the Telegraph: “I’m not saying this trial is magic. It’s an investigational medicine. We need to wait and see: will it work or not?”3
The earlier results were reported by the company, and in this source they were partway through the study (interim data)7. Outlets also describe them a little differently. The Guardian wrote that plaques were cleared in nine out of 10 people within 28 weeks3. Pharmaphorum said around 90% of people cleared plaque within 28 weeks “at higher dose levels”1. Early trials suggest trontinemab may clear amyloid faster than the approved drugs lecanemab and donanemab6, but the sources do not describe any direct comparison.
Some details also vary between sources. Organisers told UK media the trial would last four to six years3. Roche, however, has described an “event-driven” design, meaning the trial runs until enough participants show measurable decline rather than stopping on a fixed date5. A public trial listing shows the study as recruiting, with a start date of 30 November 2026 and estimated completion on 3 September 20324. That start date is later than the UK screening reports.
Who is behind it
Roche, the company that developed trontinemab, is the trial’s sponsor4. Nilforooshan is described as a consultant at Surrey and Borders Partnership NHS Foundation Trust6 and as a psychiatry consultant at the University of Surrey1. The sources do not describe his financial ties to Roche.
Roche also sells diagnostic tests. In 2025 the company promoted its own p-tau217 blood test, and its chief medical officer, Levi Garraway, described the strategy as tackling the disease “on two fronts—treatment and diagnostics”7. The sources do not say which p-tau217 test PrevenTRON uses.
PrevenTRON is one of three late-stage trials Roche is running with trontinemab. The other two, TRONTIER 1 and 2, are in people with early symptoms1. Azad Bonni, head of Roche’s neuroscience and rare disease business, said: “We are entering a new phase in this field.”5
How it fits the field
Two anti-amyloid drugs are approved for marketing: Leqembi (lecanemab) from Eisai and Biogen, and Kisunla (donanemab) from Eli Lilly1. Both are licensed in the UK but were rejected for NHS use, because their benefits were judged too small to justify the cost6.
Most earlier Alzheimer’s prevention studies recruited people with the first signs of mild memory problems. PrevenTRON instead recruits people whose thinking is still normal1. Roche is not alone. Eli Lilly has been running prevention studies with Kisunla for about four years and is also screening healthy, high-risk people with blood tests5. Jessica Langbaum of the Banner Alzheimer’s Institute said anti-amyloid drugs work better the earlier they are given, and that makes prevention studies a natural next step: “The earlier the treatment, the better the drug works.”5 Researchers also say screening with blood tests makes prevention trials more practical and cheaper than screening with brain scans5.
The need for treatments is large. Alzheimer’s causes 60% to 80% of dementia cases in the UK2. It affects around one in 14 people over 65 and one in six over 803. Changes in the brain are thought to start five to 10 years before people seek help for memory problems6.
Who can join
According to the trial listing, volunteers must be 55 to 80 years old and have no memory problems or difficulties with daily activities. Tests must also show markers that suggest a higher risk of Alzheimer’s4. People with other conditions that affect thinking, such as Parkinson’s disease, dementia with Lewy bodies or a history of stroke, cannot take part4. Participants need a study partner who can attend some visits. Visits include memory tests, blood tests and possibly brain scans4. The listing shows 34 locations, many of them in the United States4.
What to watch next
In the UK, at least 15 hospitals and clinics are expected to join by the end of the year3, including centres in Scotland and Wales6. Things to watch: how fast enrolment goes, results from Roche’s two trials in people with early symptoms, and the first results from Lilly’s prevention studies, which are expected to be the first from a large prevention trial of an approved anti-amyloid drug5. Whether trontinemab delays dementia in healthy people will not be known until PrevenTRON reads out, which is years away.
