A drug that could help to slow down Alzheimer's disease is expected to be unveiled.
Researchers are set to reveal the promising results of studies into the use of solanezumab.
It is thought that if given to patients early enough, the medication will slow down the condition.
The announcement, at Alzheimer's Association International conference in Washington, would be a landmark moment in the treatment of the disease.
Dr Eric Karran, director of research at Alzheimer's Research UK, said the drug had a "significant benefit" for people with a mild form of the disease, although "I'm not for one moment suggesting (it is) curing it".
He said: "What happened is, in the people who didn't get the drug, the people on a placebo, there was a deterioration in their disease, as we would anticipate.
"But in people who received the drug, the rate of their deterioration was slower by about 30%. So when you looked at the two groups at 1.5 years there was a clear difference between those who had been given the drug and those who didn't get the drug.
"The people who had got the drug had not deteriorated as much."
He added: "This was the first time that we have seen a benefit that really looked like it was disease-modifying."
Dr Karran previously worked for Eli Lilly - the American pharmaceutical giant behind the drug.
He told BBC Radio 4's Today programme it could still be several years before the drug is available to NHS patients.
"We still await the outcome of another phase three trial that reads out in 2016, then the drug has to go through regulatory approval which is incredibly important, then there has to be a discussion with the NHS as to whether they think this is a medicine that has an appropriate risk-benefit for it to be available on the NHS".
Around 225,000 people will develop dementia this year - a rate of one every three minutes.
Alzheimer's Society research shows that 850,000 people in the UK have a form of dementia, and that in less than 10 years, one million people will be living with dementia. This is expected to soar to two million by 2051.