Eli Lilly and Co.’s experimental Alzheimer’s drug slowed cognitive decline 34 percent in patients with mild forms of the disease, according to an analysis of Lilly’s clinical trial data by a group of academic researchers released Monday.

The magnitude of the impact fits what some physicians have said would be meaningful to patients, but Indianapolis-based Lilly still isn’t saying whether it will file for approval of the drug, called solanezumab, or instead conduct another clinical trial.

Lilly’s share price gained more than 5 percent on the news, closing Monday at $50.78.

The stock already had risen nearly 14 percent since Aug. 24, when Lilly first announced that the drug had shown some positive effects. If successful, solanezumab would be the first effective treatment for Alzheimer’s disease on the market, and could bring Lilly $5 billion to $10 billion in annual revenue.
 
“While the path forward has not been determined, we believe these data in patients with mild disease may provide a step toward a potential treatment option,” Dave Ricks, president of Lilly’s Bio-Medicines business unit, said in a prepared statement.

The drug attempts to fight Alzheimer’s disease by binding to the protein amyloid and carrying it out of patients’ brains. The build-up and clumping of excess amyloid proteins is believed to cause Alzheimer’s disease.

Lilly’s two Phase 3 clinical trials of solanezumab failed their primary goal, which was to reduce decline in the ability of both mild and moderate Alzheimer’s patient to think and do daily activities.

But in mild patients, solanezumab appeared to have some effect. In the first of the two clinical trials, solanezumab slowed cognitive decline 42 percent. But it had no effect on patients' ability to do daily activities.

In the second clinical trial, solanezumab slowed patients’ mental decline about 20 percent and their functional decline about 19 percent. However, neither result was statistically significant.

When data from both trials were pooled, the reduction in cognitive decline for mild Alzheimer’s patients was 34 percent, according to a statement released by Lilly. The improvement in daily activities was 17 percent, which was not statistically significant.

Solanezumab also showed an effect on some, but not all, so-called biomarkers, which are measurements of protein levels in patients' blood or spinal fluid. Lilly said it would present more information on the biomarker results at future medical meetings.

The data were produced by the Alzheimer's Disease Cooperative Study, a consortium of academic Alzheiemer’s researchers from around the country.

“The data results from the solanezumab Phase 3 trials were encouraging to the ADCS team,” said Dr. Rachelle Doody, a professor of neurology at the Baylor College of Medicine who presented the results Monday at a meeting of the American Neurological Association in Boston. “These results represent an important step for the medical, academic, and scientific communities in understanding brain amyloid as a target of A.D. therapies."

Dr. Martin Farlow, the associate co-director of the Indiana Alzheimer Disease Center at the Indiana University School of Medicine, said in August interview that an effective Alzheimer’s drug would need to slow patient’s decline 30 percent to 50 percent. He participated in the clinical trials of solanezumab.

“There has to be a derivable clinical benefit that’s demonstrated,” Farlow said before Lilly first released its clinical trial results for solanezumab in August. “It’s very possible that one or more of these studies may demonstrate effects that sort of point the way to the next step.”

Recent research has shown that Alzheimer’s disease begins to damage patients’ brains 10 to 20 years before they can be diagnosed with the disease. As a result, many expect Lilly will need to study solanezumab in a new clinical trial aimed at patients with pre-Alzheimer’s conditions, such as mild cognitive impairment.

Lilly officials said Monday they would continue to discuss the data from the trials of solanezumab to decide whether to file for market approval or to conduct another clinical trial.