Large-cap biotech Biogen (NASDAQ:BIIB) is somewhat of an oddball in that it's currently experiencing a rapid deceleration in revenue growth, yet Wall Street analysts are suggesting that its shares could still rise by a healthy 13.7% over the next year.

Analysts seem unfazed by the biotech's ongoing struggles with its key multiple sclerosis (MS) franchise and are apparently of the mind that Biogen has a decent shot at trumping the broader markets in 2017. So let's dissect the Street's rosy outlook, and consider if this biotech is indeed a good stock to own in 2017. 

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Biogen's next megablockbuster may be close at hand

Over the past month, Biogen's stock has gotten either upgraded, or its buy rating reaffirmed, by multiple analysts. This, perhaps, is reflecting the growing optimism that the biotech's experimental spinal muscular atrophy (SMA) drug Spinraza (nusinersen), which it licensed from Ionis Pharmaceuticals in 2013, may get the broadest label possible from the FDA (SMA Types 1, 2, and 3). As a treatment for a rare, but fatal, disorder, Spinraza will likely come with a premium pricing structure typical of so-called "orphan drugs."

But the real reason the Street is warming up to Biogen seems to be that Spinraza's peak sales could reach $2 billion in a few short years. Equally as important, the FDA is expected to grant the drug's approval on an accelerated time frame, with some analysts forecasting a regulatory decision sometime in the first quarter of 2017. That's a critical issue because Biogen's top-selling MS drug Tecfidera has been experiencing a hefty drop-off in sales in the U.S., and the company arguably can't continue to rely on price increases to drive growth indefinitely. 

In a nutshell, Spinraza could significantly boost Biogen's top line over the next five years, even after accounting for the milestones owed to Ionis under its Spinraza licensing deal and further market-share erosion within Biogen's all-important MS franchise. 

Can Biogen deliver the goods in 2017?

The fact of the matter is that everything boils down to Spinraza's regulatory fate next year. While the Street seems extremely confident that Spinraza is destined to grab a broad label for SMA early next year, the U.S. Food and Drug Administration (FDA) has been known to surprise everyone on a fairly regular basis. 

In a worst-case scenario where the FDA finds something objectionable in Spinraza's regulatory filing -- and I freely admit that this black-swan scenario appears unlikely based on the data that's publicly available -- Biogen's top-line growth would muddle along in the low single digits moving forward.

The biotech's future growth, in this case, would hinge almost entirely on the clinical success of its moonshot Alzheimer's disease drug candidate aducanumab. In other words, Biogen doesn't have a whole lot to fall back on if Spinraza doesn't pan out, or if it is significantly delayed from entering the market by the FDA. 

Putting a doomsday scenario aside, though, I'm cautiously optimistic that Biogen and Ionis will get the green light from the FDA for Spinraza sooner rather than later. And this event should pave the way for the biotech to pursue licensing deals and/or acquisitions to bolster its clinical pipeline within the next six to 12 months, creating additional layers of value for shareholders.

All told, I share the Street's bullish sentiment on Biogen, and think it could indeed outperform the broader markets in 2017 -- even though the highly unpredictable FDA remains very much part of the picture at the moment.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.