On paper, 2016 should have been a pretty good year for AbbVie (NYSE:ABBV). Revenue climbed nearly 15% year over year in the first three quarters. Earnings jumped 26% during this period from the prior year. And yet AbbVie's stock price hasn't gone up much. What's more, the new year could bring stiffer challenges for the biotech. Here are three of the biggest risks that AbbVie faces in 2017.

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Humira headwinds

Humira remains AbbVie's greatest strength and its biggest potential weakness. Sales for the drug continue to grow at a solid pace -- more than 11% year over year in the third quarter. However, Humira still accounts for 63% of AbbVie's total revenue. That puts the company at risk if any problems arise for the drug.

It's not hard to see where Humira's problems could potentially come from in 2017. AbbVie already faces indirect competition in Europe from Biogen's (NASDAQ:BIIB) biosimilars, as well as Enbrel and Remicade. William Chase, AbbVie's CFO, said in his third-quarter comments that the Remicade biosimilar wasn't making a big dent in Humira's sales and that the Enbrel biosimilar was tracking along with expectations. It could be, though, that Biogen's products might pick up momentum in the new year. 

Biogen could also win European approval for its Humira biosimilar in the coming year. There already is a Humira biosimilar approved in the U.S., but AbbVie is vigorously defending its patents and probably will be able to fend off competitors for a while.  

Rising rivals

While the threat to Humira is AbbVie's chief worry, the company also has reasons to be concerned about some of its other products. Sales for hepatitis C virus (HCV) drug Viekira are already falling in the U.S. AbbVie attributed this decline primarily to the entrance of a new competitor. Merck launched its new HCV drug, Zepatier, earlier in 2016.

Even sizzling-hot cancer drug Imbruvica could soon face the prospects of competitive pressure. AstraZeneca (NYSE:AZN) hopes to win U.S. approval for acalabrutinib in treating B-cell malignancies next year. Like Imbruvica, acalabrutinib is a Bruton's tyrosine kinase inhibitor. In a phase 1/2 study of patients with relapsed/refractory chronic lymphocytic leukemia, acalabrutinib appeared to have a better safety profile than Imbruvica. 

If AstraZeneca wins approval, AbbVie could have a real fight on its hands. The company is fully aware of the potential threat from acalabrutinib and is moving to quickly advance Imbruvica into other indications to stay ahead of AstraZeneca.

Pipeline problems

The perennial risk for AbbVie (and any other drugmaker, for that matter) is from problems with pipeline candidates. Regulatory agency rejections and late-stage clinical failures present the biggest threats.

AbbVie's pipeline currently includes 12 late-stage programs. The biotech expects to submit Elagolix for approval in treating endometriosis next year. AbbVie also hopes to get a green light for commercialization of its next-generation HCV therapy in 2017.

Results are expected to be announced in the coming year for three clinical studies of experimental autoimmune disease drug risankizumab. The company should also read out data from several clinical studies that could lead to regulatory filings for new indications for Imbruvica and Venclexta.

At this point, all of these programs look promising. However, it's not unheard of for once-promising pipeline candidates to flop in late-stage studies.  

Weighing the risks

AbbVie investors should be most concerned about potential threats to Humira. The company still depends so heavily on this one product that any bumps in the road make a big difference to its bottom line.

AstraZeneca could very well present a formidable challenge to Imbruvica. I wouldn't be too worried about the impact in 2017, though. Acalabrutinib will probably be a bigger problem over the longer run.

I'm least worried about pipeline problems. It's not that I don't think AbbVie couldn't have a setback. However, I suspect the biotech is in pretty good shape overall with its pipeline.

Even with these real risks, AbbVie should continue to be a solid pick for investors -- at least while the company can stave off competition to Humira in the U.S. AbbVie still presents a good opportunity for growth while paying one of the better dividends around. I think 2017 will likely be an even better year for the company than 2016 has been.