A drug could provide a breakthrough for Alzheimer's disease within the next five years, UK scientists have said.
People aged 55 to 90 are currently being recruited to a final-stage study in the US, which will examine if the drug solanezumab slows the cognitive and functional decline of people with mild Alzheimer's.
Previous trials of the drug - made by pharmaceutical giant Eli Lilly - have shown no effect in people with later stages of the disease but there are signs it could be effective at an earlier stage.
Researchers found the drug had an effect on daily behaviour and functioning of brain and memory in people with earlier-stage disease.
In the new trial, people will be given solanezumab as a monthly 400mg injection for 18 months.
The trial is expected to end in December 2016.
Dr Eric Karran, director of research at Alzheimer's Research UK, said scientists were "full of hope" that a breakthrough could come within five years.
He said the results may suggest that monthly injections should be given early to ward off the disease - in the same way that people take statins to prevent heart disease.
Dr Karran said the drug had been shown to have a "reasonable" effect in people with mild Alzheimer's and results would come within five years.
"I think the pathway now is if solanezumab is shown to work in mild Alzheimer's disease then the pathway would be to give it earlier and earlier and earlier...and you could have confidence you will see an effect."
Dr Karran said changes in the brain associated with dementia can happen as much as a decade before first symptoms arise.
He said: "I am full of hope that we are going to have a breakthrough in five years."
Prof Nick Fox, from the Institute of Neurology, at University College London, said that preventing disease before symptoms were present offered the best "window of opportunity" to halt the impact of disease.
A spokeswoman for the Alzheimer's Society said: "The news that solanezumab is going to be looked at again is encouraging.
"As it stands there's a shockingly low number of clinical trials focusing on dementia.
"To change this and give people with dementia better hope of effective treatments, much more investment in this area is needed.
"The upcoming G8 summit on dementia provides us with a fantastic opportunity to gain global collaboration in research and much needed funding commitments from government."