What happened

Biotech heavyweight Biogen (NASDAQ:BIIB) failed to follow the broader industry higher last year. Despite biotech stocks at large posting market-beating gains in 2019, Biogen's shares actually lost 1.4% of their value last year, according to data from S&P Global Market Intelligence

So what

Biogen's stock lost ground for three key reasons in 2019:

  1. The company's core multiple sclerosis franchise essentially flatlined from a revenue generation standpoint. 
  2. Although Biogen did reel off a handful of important business development deals in 2019, the company didn't pursue a bolt-on acquisition that would immediately change its near-term outlook. 
  3. Biogen's decision to pursue a regulatory approval for its controversial Alzheimer's disease drug candidate, aducanumab, failed to win over the whole of the investing community. Most industry insiders, in fact, think that the Food and Drug Administration will ultimately reject the drug. 
Wooden blocks displaying an array of healthcare symbols stacked in a pyramid on a wooden table.

Image source: Getty Images.

Now what

Even though Biogen hasn't even filed for aducanumab's approval, the biotech is reportedly already gearing up for the drug's potential launch. That's a rather surprising move, given that aducanumab faces an uphill battle on the regulatory front.

The key takeaway, though, seems to be that management probably won't pull the trigger on a major acquisition in 2020. Avoiding the numerous pitfalls associated with costly merger-and-acquisition deals could turn out to be a stroke of genius -- that is, if regulators unexpectedly give the thumbs-up to aducanumab.

But the flip side is that Biogen will be behind the eight ball in terms of business development in the event that aducanumab turns out to be a dead end. Therefore, investors may want to take a wait-and-see approach with this large-cap biotech stock this year.