For decades, every tale in the world of Alzheimer's drug development has followed the same story arc: first a period of hope, expensive effort, and no small amount of brilliance. Then, a series of clinical trials that reveals that the candidate treatment isn't effective against the disease. So it seemed to be this spring for Biogen's (BIIB 0.94%) aducanumab. The company ended its trial of the drug because it didn't seem to work. But last week, it revealed positive new data, and said it would ask for FDA approval of aducanumab, which put a rocket under its stock price. In this segment of the Oct. 25 Motley Fool Money podcast, host Chris Hill and senior analyst Ron Gross consider just how extraordinary this turn of events is, and offer up an opinion on the obvious question for investors: Is it too late to buy in to Biogen?

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This video was recorded on Oct. 25, 2019.

Chris Hill: Shares of Biogen up 30% this week. The biotech company posted some good third quarter results, but it was Biogen's separate announcement about a potential treatment for Alzheimer's disease that had the stock on the rise. Ron, what's the story?

Ron Gross: So interesting! Drug comes back from the dead. Potentially huge for Biogen. But really, huge for the world. In March, the company said a major trial for the drug -- let's all pronounce this together, ready? -- Aducanumab had been a failure, but they kept collecting data. And as the data rolled in, they saw a positive signal from the group that was getting the highest dose of the drug, which is potentially really exciting. It helps patients with cognitive function and their ability to perform basic tasks. Now, Biogen is going to actually ask the drug regulators to approve the drug. That's going to take some time. It takes a year, two years plus. But they're pretty sure that the signals that they're getting are going to be the first drug to really help Alzheimer's patients. Very huge for Biogen. Huge for sufferers all over the world. Could be potentially very exciting. Let's temper our enthusiasm just a bit because they've got some hurdles to go through here. These approvals are not so easy. But if this goes through, it's really a humongous thing. 

Hill: I want to come back to the stock in a second. But first, I'll preface this by saying, Ron, I know you're not an expert when it comes to biotech companies. 

Gross: Thank you for that!

Hill: But I'm curious, how unusual is this procedure? The idea that any company, whether it's Biogen or someone else, would essentially shut down a trial, but still collect data, and then come back and say, "Actually, we want to give this another shot"?

Gross: I think it's relatively common that they do keep collecting the data, for sure, as it comes in. And they do analyze it as well. It's rare, however, that what they see subsequent is different from what they saw initially. I should say, it's really because the people getting the highest dose of the drug is where they saw the signal here. And perhaps the initial data was not of those people. This is pretty rare. I think that's why the regulators will probably actually scrutinize this even more than normal. But maybe, because it's so important, because it's Alzheimer's related, we'll actually get a fast track of some sort.

Hill: Shares of Biogen had been down for the year. This week erased that loss completely. When you look at shares of Biogen, is this an expensive stock? Or does this still have room to run?

Gross: Even though it's a biotech or a pharmaceutical drug company, you can't think of it as one of these early stage biotechs that are pre-revenue. 

Hill: It's a $50 billion company.

Gross: Extremely profitable company. Now, companies like this actually don't trade at very high multiples. Biogen is around 9X earnings right now. The average company trades around 11X. So, maybe it's a little cheap relative to the peers. But these companies don't get the high multiples.