Investors eagerly awaited Biogen's (NASDAQ:BIIB) presentation on its investigative Alzheimer's drug at Thursday's Clinical Trials on Alzheimer's Disease conference. They were hoping for clues about whether or not the U.S. Food and Drug Administration (FDA) will see the new drug in a favorable light.

The result? Those who strongly believed in the data prior to the report believed in it even more, those who were skeptical became even more skeptical, and those who were on the fence stayed there.

Two scientists in a lab holding and mixing bottles and test tubes with liquid in them.

IMAGE SOURCE: GETTY IMAGES.

Let's back up a few weeks for some context. Biogen shocked investors in October when it announced that it would submit aducanumab to the FDA for approval early next year. Months earlier, the biotech company stopped trials of the drug after an analysis determined that it wouldn't work. But a look at additional data reversed that decision.

The company's shares rose 26% on the day of the announcement, and investors waited for the December conference when Biogen said it would share further information.

Higher doses reduced clinical decline

Aducanumab acts by binding to and eliminating beta amyloid, a protein that clings to neurons in the brains of Alzheimer's patients. In Thursday's presentation, Biogen explained that earlier data, which didn't meet endpoints and resulted in halting trials, involved giving the drug at lower doses.

In patients with a gene variant that increases a side-effect risk, researchers started with lower doses of the drug, then later increased the doses when it was deemed safe to do so. Therefore, that study, called Engage, had fewer participants getting high doses for the full treatment period compared with Emerge, the second study. In Emerge, the high dose of aducanumab reduced clinical decline, while in Engage, only the subset of patients given high doses showed the same result.

While experts involved in the trial expressed excitement and optimism, some analysts remained cautious. Mizuho Securities' analyst Salim Syed described the data as "not impressive." Jefferies' analysts wrote, "the statistics and overall rules on getting a drug approved don't appear to be met here and so this comes down to a review and discussion with FDA."  

Record drug approvals

Still, the fact that there aren't currently any treatments for the disease that affects more than 5 million Americans could support the case for aducanumab's approval. A report in the Boston Business Journal referred to past cases in which patients pushed for cancer or HIV treatments resulted in approvals of "good enough" drugs. Statistics showing a decrease in FDA rejections also might help Biogen's case. The Center for Drug Evaluation and Research approved 59 novel drugs last year, a record number, and approvals more than doubled from 2016.

So what does all of this mean for investors? Biogen's shares slid 3% after Thursday's data, then rebounded to close with a 3.5% gain. That performance may hint at what investors will see ahead of a submission to the FDA and any potential approval or rejection, as many question whether the trial results are solid enough to merit approval.

Biogen shares have rebounded about 35% from this year's low in August, but it seems premature to bet on a steady share recovery at this point -- at least based on aducanumab news. For investors looking for an entry point into Biogen stock, there still might be some waiting to do.