A drug to treat multiple sclerosis has undergone successful trials showing its ability to slow damage to the brain, scientists have said.
Researchers testing ocrelizumab reported positive results in the treatment of primary progressive MS, a particularly aggressive form of the disease.
The results, published in The New England Journal of Medicine, showed that 33% of patients taking the drug deteriorated over time compared with 39% of those taking a placebo.
Patients taking the drug also displayed less brain loss in scans, and scored better on the time needed to walk 25ft (7.6m).
Writing in the journal, Dr Peter Calabresi, from Johns Hopkins University in Baltimore, said: "This is the first drug to show a significant effect in slowing disability progression in a phase three trial in primary progressive multiple sclerosis, and therefore the trial represents a landmark study in the field."
More than 100,000 people in the UK have MS.
The research involving testing on more than 700 patients by scientists at institutions across the US and Europe. It was sponsored by ocrelizumab's manufacturer, Roche.
The drug has been accepted for review for use by the European Medicines Agency and the US Food and Drug Administration.
Two further trials also showed the drug's ability to treat relapsing multiple sclerosis, characterised by distinct attacks which come and go.
Dr Aisling McMahon, head of clinical trials at the MS Society, said: "This is really big news for people with the primary progressive form of multiple sclerosis. It's the first time any treatment has shown the potential to reduce disability progression for this type of MS, which offers a lot of hope for the future.
"MS can be challenging and unpredictable and the 15,000 people in the UK living with primary progressive MS currently have no treatments available to slow the worsening of their condition."