Biogen Inc on Thursday presented new data on its experimental Alzheimer's drug aducanumab that did not reveal any new safety concerns.

The U.S. biotech company made the case to researchers and investors about why it plans to seek U.S. approval after declaring the drug a failure in March.

Experts had been watching closely for any statistical abnormalities or excess safety issues that would affect how the drug is reviewed by the U.S. Food and Drug Administration, likely in the second half of 2020.

Biogen's shares (BIIB) had been halted prior to the presentation at a Alzheimer's meeting, reopened lower, and then rose as investors tried to parse the meeting from the complicated study. The stock was last up 1 percent.

It's been at least 15 years since the FDA has reviewed an application for a new Alzheimer's treatment, and an agent that can slow progression of the mind-wasting disease is desperately needed.

Biogen has partnered with Japan's Eisai Co Ltd to develop aducanumab as well as BAN2401, which works in a similar way.