Biogen Idec released much anticipated results from a study of a potential Alzheimer’s disease treatment on Friday, showing that it slowed cognitive decline in some patients.

In December, the biotechnology company based in Cambridge, Massachusetts, said the developing drug aducanumab reduced a type of plaque in the brain believed to play a key role in the disease and slowed clinical impairment in patients with a mild form of the disease.

Data from the 166-person study had already prompted the company to accelerate development and make plans to skip directly to a much larger late-stage study.

In the study, patients receiving the largest dose of the drug showed significant improvement over patients receiving a placebo. The drug candidate also met safety goals.

Typically, early-stage studies focus mainly on safety. The late-stage study will be much larger and focus more closely on efficacy and is generally the final phase before a company submits a drug to regulators for approval.

There is no cure for Alzheimer’s disease, the most common form of dementia. About 35 million people worldwide have Alzheimer’s, and current treatments only temporarily ease symptoms. The causes of the disease are still not very well understood and drugmakers have tried – and failed – for years to develop a treatment.

Last summer, biotech drug developer Genentech said its experimental drug failed to slow mental decline in midstage studies on more than 500 people with mild to moderate Alzheimer’s disease. But the treatment showed some promise in patients with a milder form of the disease who received a higher dose.

In 2012 a potential treatment called bapineuzumab developed by Pfizer, Johnson & Johnson and Elan Pharmaceuticals failed.

Biogen was to present the data on aducanumab on Friday at the 12th International Conference on Alzheimer’s and Parkinson’s Diseases and Related Neurological Disorders in Nice, France.