Eli Lilly and Co said its experimental Alzheimer's drug slowed cognitive decline in patients with a mild form of the disease, though it failed key trial goals, sending shares up as much as 8 percent on hopes the treatment may be salvaged.

The late-stage trials, known as EXPEDITION 1 and 2, tested solanezumab in patients with mild-to-moderate Alzheimer's disease, compared with a placebo.

A secondary analysis of the results showed a statistically significant slowing of cognitive decline in patients with mild Alzheimer's disease, but not in those with moderate Alzheimer's, the company said on Friday.

"We recognize that the solanezumab studies did not meet their primary endpoints, but we are encouraged by the pooled data that appear to show a slowing of cognitive decline," said Lilly Chief Executive John Lechleiter. "We intend to discuss these data with regulatory authorities to gain their insights on potential next steps."

Lilly shares climbed 4 percent to $44.10 in early trading on the New York Stock Exchange, after earlier gaining as much as 8 percent.

The results bolstered hopes the treatment may still prove viable for patients either at an earlier stage of the disease, or who have yet to show symptoms.

"Basically the odds of approval just went up from like 10 percent to maybe 20 to 30 percent," said Mark Schoenebaum, analyst with ISI Group, noting that patients with a mild form of the disease comprise at least half of the diagnosed population. "(That's) still high risk, but much better than expected."

Lilly's drug aims to reduce a toxic protein found in the brains of Alzheimer's patients, known as beta amyloid.

Pfizer Inc and Johnson & Johnson earlier this month said their similar drug, bapineuzumab, failed in late-stage trials to improve memory or thinking skills in patients with mild and moderate forms of the disease.

Sanford Bernstein analyst Tim Anderson said the Lilly results on Friday supported a theory that such treatments "probably need to be given as early as possible in the course of the disease."

"At this point, theoretically all possibilities are still on the table," Anderson wrote in a research note. "This includes the possibility that solanezumab could be filed for regulatory approval, given the large unmet medical need in patients with Alzheimer's disease and the generally acceptable safety profile."

"Our best guess is that more studies would have to be done before FDA or other regulatory agencies would consider approving solanezumab," he said.

Alzheimer's is the most common form of dementia and the sixth leading cause of death in the United States. An estimated 5 million Americans are believed to have the disease.

The Lilly trials tested solanezumab in more than 2,050 patients in 16 countries, over an 18-month period. Patients on the drug also experienced adverse events such as lethargy, rash, malaise and angina, compared to the placebo.

The company said more detailed data will be presented at medical meetings in Boston and Monaco in October.