What happened

Shares of Amarin (NASDAQ:AMRN) jumped just shy of 17% last month, according to data from S&P Global Market Intelligence. The entire share-price increase was compressed into the last week of February as investors anticipated the company's fourth-quarter 2018 earnings conference call on the second to last day of the month. Analysts knew revenue growth would continue to chug along as sales of Vascepa continue to grow -- and they were right. 

Amarin reported fourth-quarter 2018 revenue growth of 44% year over year on sales of $77.3 million. Full-year 2018 revenue settled at $229.2 million, marking a 27% increase from the previous year. While that's an impressive growth rate and one expected to pick up in 2019, investors are waiting for Vascepa to be approved for broader use -- a milestone that could usher in a multibillion-dollar sales opportunity. However, management said shareholders will need to remain patient.

A man drawing an ascending graph.

Image source: Getty Images.

So what

On the fourth-quarter 2018 earnings conference call, management said it expects full-year 2019 revenue in the neighborhood of $350 million. But nearly all of that revenue growth will come from currently approved indications of Vascepa.

While Amarin is optimistic about its chances to earn expanded marketing approval for the drug to help patients with elevated triglyceride levels reduce their cardiovascular health risks, that regulatory decision isn't expected to be handed down until late 2019 or early 2020. In other words, investors lucky enough to have enjoyed the stock's epic 500% rise in the last year on the heels of impressive late-stage clinical results will have to wait just a bit longer.

Now what

Amarin shares are historically expensive, but that's not unexpected. The potential for Vascepa to be taken by millions of Americans at higher risk of developing cardiovascular disease would make it a blockbuster drug (read: at least $1 billion in annual sales). Analysts expect the drug to reach peak annual sales of $2 billion, although that could be a significant underestimate, according to Motley Fool contributor George Budwell.