This week in January usually brings lots of excitement thanks to the annual J.P. Morgan Healthcare Conference. And that's exactly what happened over the last several days. News and rumors propelled several biotech stocks a lot higher.

Three of the big biotech winners of the week were Insmed (INSM -0.38%)Amarin (AMRN -0.49%), and Clovis Oncology (CLVS). What lit a fire beneath these stocks? And are they smart picks for investors to buy now?

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1. Insmed

Insmed's share price skyrocketed 53% higher this week. The biotech presented at the J.P. Morgan conference on Wednesday, but Insmed's announcement after the market closed on Jan. 4, 2019, provided a big boost for the stock on Monday.

The company provided a sneak peek at its Q4 results. Sales of Arikayce are expected to come in at $9.2 million. The antibiotic won approval from the Food and Drug Administration on Sept. 28, 2018. The good start for Arikayce and hints that even greater momentum could be on the way generated enthusiasm among investors.

Insmed said that more than 500 patients had initiated treatment with Arikayce, but 600 physicians had written at least one prescription for the drug as of the end of 2018. This implies that there are plenty of patients who will begin treatment in early 2019, which could point to a strong first quarter for Insmed.  

Check out the latest Insmed earnings call transcript.

2. Amarin

Amarin stock vaulted 36% higher this week due to a couple of catalysts. The stock enjoyed a boost from the biotech's presentation at the J.P. Morgan conference on Thursday. Amarin also benefited from speculation that it could be an acquisition target.

Rumors swirled in the latter part of this week that Pfizer (PFE -0.34%) is interested in making a play for Amarin. The big attraction, of course, is Amarin's triglyceride-lowering drug Vascepa. Amarin attracted a lot of attention in November from its announcement of overwhelmingly positive results from a cardiovascular outcomes study that showed Vascepa significantly reduced cardiovascular risk. 

Although the rumors haven't been substantiated yet, Amarin appears to be a good fit for Pfizer. The big drugmaker has a strong presence in the cardiovascular and metabolic diseases market. Pfizer's new CEO, Albert Bourla, stated at the J.P. Morgan event this week that the company is interested in doing deals that aren't distracting. It's possible that the size of a potential buyout of Amarin could meet Bourla's criteria. 

Check out the latest Amarin earnings call transcript.

3. Clovis Oncology

Shares of Clovis Oncology jumped 31% this week. Like Insmed, Clovis provided a preliminary look at its Q4 results, and investors liked what they saw.

The biotech stated that its flagship product, ovarian cancer drug Rubraca, generated between $30.3 million and $30.8 million in the fourth quarter. Clovis Oncology CEO Patrick Mahaffy highlighted this performance in his comments at the J.P. Morgan conference on Tuesday.

Perhaps the best news for Clovis is that Rubraca's sales should pick up even more in 2019. The biotech recently received a positive recommendation in Europe for its second ovarian cancer indication. It successfully defended its key European patent for Rubraca. Clovis also hopes to pick up an FDA approval for the drug in treating prostate cancer by the end of this year.

Check out the latest Clovis Oncology earnings call transcript.

Are they buys?

I suspect that all three of these biotech stocks could continue to perform relatively well in 2019. That doesn't necessarily mean that they're great picks to buy for most investors, though. Tremendous growth expectations are already baked into the share prices for Insmed, Clovis, and Amarin. 

My hunch is that Clovis Oncology has the least upward potential unless Rubraca sales really kick into high gear this year. And while Arikayce should be a big winner, it's still really early for Insmed. 

Amarin is the most intriguing of these biotechs, in my opinion. I don't think investors should scoop up shares just because of rumors of a potential acquisition. However, there are solid reasons why Pfizer or other big drugmakers could be interested in buying Amarin, most importantly that Vascepa could become a megablockbuster.

Sure, Amarin's market cap already tops $5 billion. I think the company should be worth considerably more if Vascepa reaches its potential. I think Amarin is a stock to consider buying for aggressive investors.