Several biotech stocks started off with a bang in 2018. If the first week of the new year is any indication of what's to come, biotech stocks could be in store for big gains like 2017 delivered.

Three biotechs, in particular, enjoyed tremendous performances over the last few days: Sorrento Therapeutics (NASDAQ:SRNE), ChemoCentryx (NASDAQ:CCXI), and Insys Therapeutics (NASDAQ:INSY). Here's what drove these stocks higher this week -- and whether any of them appear to be smart picks for investors.

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Sorrento Therapeutics

Sorrento Therapeutics stock skyrocketed nearly 50% this week. What was the big news? The only announcement from Sorrento came on Tuesday -- and it shared that the company's CEO, Henry Ji, would be presenting at a conference in San Francisco this weekend. While that might not sound like a big deal, investors probably liked what Ji would be discussing: Sorrento's chimeric antigen receptor T cell (CAR-T) technology.

CAR-T is hot these days in the biotech world. Gilead Sciences shelled out $11.9 billion several months ago to acquire Kite Pharma to get its CAR-T pipeline. Other biotechs with CAR-T programs have seen their valuations soar. So has Sorrento. The biotech's market cap has more than doubled over the past month and tripled over the last three months. 

The difference for Sorrento is that its CAR-T approach doesn't use viruses. Although the biotech has only conducted preclinical studies so far, there are several potential advantages to nonviral therapies, including being quicker to develop and possibly eliminating the need for a lengthy monitoring period of patients after treatment. 

ChemoCentryx

ChemoCentryx stock jumped around 40% this week. The biotech made two announcements on Thursday that served as catalysts.

One update was that the European Medicines Agency (EMA) had accepted the conditional marketing authorization (CMA) application for avacopan for review. Avacopan targets treatment of anti-neutrophil cytoplasmic antibody (ANCA) associated vasculitis. ANCA-associated vasculitis is a group of highly inflammatory autoimmune and progressive rare diseases that are often fatal.  

This announcement tied into ChemoCentryx's other one. Because of the EMA's acceptance of the CMA application for avacopan, the biotech will receive a $50 million milestone payment from its partner, Vifor Fresenius Medical Care Renal Pharma, which is owned by Vifor Pharma and Fresenius Medical Care. In addition, ChemoCentryx announced that it had entered into a $50 million financing agreement with Hercules Capital, Inc. The combination of these developments put the small biotech in much better financial shape. 

Insys Therapeutics

Insys Therapeutics stock ended the week up more than 20%. But the biotech's gains were much higher -- over 50% -- earlier in the week.

On Tuesday and Wednesday, Insys stock was on a roll, up by double-digit percentages both days. Why? The best bet is that a short squeeze was underway. Insys stock was hammered throughout much of last year, with sales for its opioid painkiller Subsys tanking and federal investigations into its promotional practices. The biotech reported a few positive developments in December, though, that seem to have caused some naysayers to begin covering their short positions. And Insys stock was off to the races, soaring over 80% last month prior to the huge gains this week.

The euphoria from short squeezes tend to wear off pretty quickly, however. That appears to be what happened with Insys. On Thursday, the stock gave up a big chunk of its new year's gains. Still, Insys has doubled from where it was at the beginning of December.

Are they buys?

Are any of these hot biotech stocks decent picks after their huge gains? It depends on how much risk you're comfortable with.

Sorrento doesn't have any products on the market yet. However, the FDA should hand down its decision on approval for topical pain drug ZTlido by Feb. 28, 2018. Sorrento's nonviral CAR-T approach is the more intriguing wild card for the stock in my view, though. My concern is that it's still really early for the biotech's CAR-T program. I'm not ready to call Sorrento a stock to buy, but it's definitely one to watch closely.

ChemoCentryx also looks interesting. Avacopan probably has a good shot at winning approval in Europe and the U.S. for treating ANCA-associated vasculitis. The drug is also being evaluated for treating two additional rare diseases. ChemoCentryx's pipeline includes several other phase 1/2 programs. There are definitely risks that neither Avacopan or these other programs will pan out, but I think the risk-reward proposition for ChemoCentryx is reasonably attractive.

That leaves Insys. In October, I singled the stock out as possibly the biggest comeback story of 2018. My timing was a little off, but Insys certainly has mounted a major comeback since December. I think that sales will stabilize for Subsys this year. I also expect some pickup in momentum for new cannabinoid drug Syndros. In my opinion, Insys remains one of the best cannabinoid-focused biotechs on the market. I think it's still a buy. 

Keith Speights owns shares of Gilead Sciences. The Motley Fool owns shares of and recommends Gilead Sciences. The Motley Fool has a disclosure policy.